CORNELL UNIVERSITY LIBRARY BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN 1891 BY HENRY WILLIAMS SAGE Cornell University Library QB 44.M97 A beginner's star-book; an easy guide to 3 1924 012 302 588 DATE DUE ^^fi*ii**20Or PRINTCOINU 5 A. Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924012302588 SPIRAU NEBULA IN URSA MAJOR, KNOWN AS MESSIER 101 From a photograph taken at ike Mt. Wilson Solar Observatory A BEGINNER'S STAR-BOOK An Easy Guide to the Stars and to the Astronomical Uses of the Opera-Glass, the Field-Glass and the Telescope By KELVIN McKREADY With Charts of the Moon, Tables of the Planets, and Star Maps on a New Plan Including Seventy Illustrations G. P. PUTNAM'S SONS NEW YORK AND LONDON trbe iRnfcfterbocfter ipress 1912 VVi, ■^ Q6 H Copyright, igi2 BY G. P. PUTNAM'S SONS £ tCbe Itnlcfterbocliec prces, Dew Vocft Uo M. AND D. AND G. WHO HAVE WATCHED WITH ME AT THE THRESHOLD No unregarded star Contracts its light Into so small a character, Removed far from our humane sight, But if we steadfast looke We shall discerne In it, as in some holy booke How man may heavenly knowledge leame. William Habington, 1634. " Some amateurs, I am told, believe that their efforts are rendered futile by the more power- ful equipment and better atmospheric advantages of other investigators. If this feeling were well grounded, it might fairly be asked whether the great observatories are worth their cost. For the history of astronomy teaches that much of the pioneer work has been done by amateurs, usually with modest means and in unfavorable climatic conditions. We may therefore inquire whether useful work of such a nature as to contribute in important degree to the advancement of science can still be done with simple and inexpensive instruments. This question may at once be answered in the affirmative. Far from believing that recent developments have been detrimental to the amateur, I am strongly of the opinion that his opportunities for useful work have never been so numerous." — A Study of Stellar Evolution, by George Ellery Hale, Director of the Mt. Wilson Observatory, pp. 243; 23; University of Chicago Press, 1908. preface This book has been made in the hope that it will prove of service. It is, in a sense, but one effort more to help those who are without technical equipment to claim through the unaided eyes, or through simple optical instruments, their heritage in the things of the sky. And yet the book would not have been undertaken but for the conviction that it represents certain new and useful departures in scope and method. For a fuller state- ment of these I must refer to the introductory pages. While intended for the general reader I trust it may also prove of value in some of our educational institutions. Many a teacher of sound culture and adequate training who would like to observe and would like to help others to observe, has had no opportunity to know the use and possibilities of the small telescope. Most of the manuals of obser- vation assume as already known many of the things that the beginner chiefly desires to know — both as to the stars and the instruments employed. In dealing with the practical side of observation I have tried, therefore, to be explicit and to be definite. I have not avoided repetition but have tried to employ it in the in- terest of clearness and usefulness. I have attempted also to meet the small problems the very existence of which — when once overcome — the experienced observer has been alto- gether too likely to forget. I have not given the volume the form or manner of the text-book; for, as already stated, it is especially intended for the general reader. And yet as a book for supple- mentary use, and as a simple observational manual, it may be employed concurrently with any of our modem volumes on astronomy. It is not unlikely that a little actual experience in observation will give broader value to the use of such texts both by the general reader and by the student, and may add an interest to the theory and mathematics of the science. Even where there is no formal course in "astronomy," the student will find a real gain to pleasure, to imagination, and to a larger conception of the universe in the mere experience of intelligent observation. It is worth while to know something of the things of the sky, not merely from a picture or a lantern slide, but with that sense of actuality which comes from seeing the things themselves. The volume is also intended for those who wish to add to their knowledge of the skies without optical aid of any kind. Even to readers unable to use a telescope, the information as to the telescopic objects among the stars, in the moon, etc., is of interest and value. While, therefore, such information is kept distinct, it is presented in close connection with the more popular discussion of the moon, the planets, and the constellations. Tables are included indicating the positions of the planets in their course through the stars, month by month, till the year 1931. The telescopic objects are grouped directly under the Key-Maps in three different classes, — (a) those for the opera-glass and field-glass; (h) those for telescopes of 2 inches, and (c) those for telescopes of 3 inches, in aperture. Though almost all the selected objects are, therefore, extremely easy, they nevertheless afford abundant opportunity for larger instruments. Indeed, I trust that advanced students will not find the general apparatus of the book, its diagrams, maps, etc., unsuited to their needs, — for great care vi preface has been taken to preserve accuracy of statement, to avoid the making of a mere "wonder- book, " and to keep the volume in touch with the better sources of information. Much of it is, necessarily, a recapitulation of elementary facts; it is frankly a book for "the be- ginner"; and yet I have worked in the conviction that the beginner is peculiarly entitled to soundness and sobriety of statement. The facts themselves are sufficiently interesting, without embellishment or exaggeration. How much of success has been attained I cannot judge. The whole literature of the subject is so replete with detail that it is impossible wholly to eliminate the factor of error. Those who know the subject best will, therefore, be the most generous in judgment; for these will know, as none others can, what to the author must be the labor-cost of even so elementary an undertaking. Many of my obligations are expressed in the brief bibliography at the close of the volume. The data as to star magnitudes are, for the most part, from the Revised Harvard Photometry (1908). For the measures of double stars, for the magnitudes of components not given in the Harvard Photometry, and for much other technical information I am in- debted to the Sternverzeichnis of Ambronn (Gottingen, 1907). The results there given are, of course, largely compilations from Bumham and from other sources, but the volume is none the less admirable as a general summary of stellar information. For the data as to the distances of the stars I am indebted to the List of Parallax Determinations by Kapteyn and Weersma (Groningen, 1910). The plan for showing the stars in a dark sky, with key-maps to the same scale, was first suggested to me by Miiller's Atlas to his Kosmische Physik. Supplementing this general method with certain features suggested in The Midnight Sky (by Dunkin of the Greenwich Observatory, 1872), and adding certain practical features gained in the personal experience of observation, I have tried to se- cure a composite result — a result based upon sound precedents and yet representing a real advance in the mapping of the skies for popular use. Of the specific plan and method of the maps I have written at length in the introductory pages. In closing these brief acknowledgments I must record my thanks to the Yerkes Obser- vatory, to the Mt. Wilson Observatory of the Carnegie Institution, to the Lick Obser- vatory, and to Dr. Percival Lowell, Director of the Lowell Observatory, for the use of photographs. I wish also to thank my friend, Mr. Burtis B. McCam of Chicago, for much admirable work in the drafting of the maps; and finally I would say that in the arrangement, plotting, and articulation of the maps and diagrams, and in the assembling of the technical data, I am indebted to the cooperation of a devoted hand to which I am not permitted to make public acknowledgment, but to the generosity of which I am something more than grateful. K. McK. New York City, January, 1912 A.D. Contents PAGE I. Introduction . i OUR HERITAGE IN THE STARS THE SKY AND ITS MAPS. II. Objects to be Seen. i. — The Stellar World 9 WHAT ARE THE STARS? — STAR MAGNITUDES AND STAR SYMBOLS THE DOUBLE STARS — THE VARIABLES STAR COLORS AND STAR CHARACTER THE CLUSTERS AND NEBULA. III. Learning to Observe ..... . . . 22 FOUR KEY-GROUPS LOOKING NORTH, ALL SEASONS — LOOKING SOUTH, NOVEMBER TO APRIL — LOOKING SOUTH, APRIL TO AUGUST — LOOKING SOUTH, JUNE TO NOVEMBER. IV. Star- Maps for Any Year . . . . 30 THE USING OF THE CHARTS, SOME PRACTICAL SUGGESTIONS — A TIME SCHEDULE FOR ALL HOURS — NIGHT-CHARTS AND KEY-MAPS, TWENTY-FOUR PLATES WITH ACCOMPANYING TEXT. V. Objects to be Seen. ii. — The Solar System . . . . . . 62 THE SUN — THE MOON, WITH FOUR PHOTOGRAPHS AND THEIR KEY-MAPS — THE PLANETS, AND TABLES FOR FINDING THEM COMETS AND METEORS. VI. Some Instruments of Observation ..... 97 THE OPERA-GLASS THE FIELD-GLASS — THE HAND TELESCOPE, OR SPY-GLASS — THE ASTRO- NOMICAL TELESCOPE, SELECTING IT AND USING IT — THE VALUE OF LOW POWERS — HINTS FOR THE BEGINNER. VII. An Observer's Catalogue of Telescopic Objects . . . .116 VIII. Statistical Tables of Star Distances, etc 138 IX. Index 147 X. Additional Maps ; the Celestial Sphere North and South . A BEGINNER'S STAR-BOOK H. llntrobuction Our Heritage in the Stars My first impulse was to name this book "The Stars — with Astronomy left out." I have not done so, and yet such a title would represent no serious misstatement of its purpose. It is a purpose sincerely consistent with the most grateful estimate of astronomy as a science. But just as there may be a pleasurable familiarity with the flowers, without any very great knowledge of botany, so there may be a pleasurable knowledge of the stars without any very large acquaintance with the technicalities of astronomy. Indeed the pleasure of the stars may be the pathway to their science, just as a homely, familiar knowledge of the flowers will often lead to an understanding of their botany. Such a suggestion is in harmony with the better and happier educational methods of our time. We are learning to awaken and develop the natural enthusiasms which make the true geologist by taking our classes into the hills and the fields ; we are teaching natural history by seeking to interest the beginner in the animal life about us. In almost every department of education we are now trying to go, first of all, to the objects themselves; and we are seeking to build up our knowledge less upon a basis of discipline and convention and more upon a basis of interest. And yet in astronomy we still find, altogether too often, that the pupils in our schools are compelled to busy themselves with the angles and circles of the celestial sphere, with the grim mystery of solstices and nodes, before they have been brought face to face with the friendly realities of the sky. So is it, also, with the general reader of adult years — for whom this book is more es- pecially intended. Even our more popular manuals of astronomy too frequently assume that the mathematics of the science are already known, — or, if not already known, must necessarily be learned. There are many pathways to the pleasure of the stars. To the minds of some the way of mathematics may be, instinctively and naturally, the best method of advance. Some of the greatest of astronomers — such as Newton himself — were primarily mathematicians and were never very great observers. But for most of mankind, observation in its most elementary sense — observation finding its primary impulse in the simple pleasure it awakens — -must be the method of approach. The purpose of this book is, therefore, to take the reader directly into the presence of the stars, showing the beginner when to look and where to look, and what there is to see. As knowledge is increased, the field of interest is enriched. While the volume is an attempt to begin with the beginner, it also attempts to go on with him. It seeks to pro- vide, at least in some measure, for the larger interests that may be awakened. Without intruding into the field of theoretical astronomy, I have thought it well to add, in the chapter devoted to each subject, such general information as may help to quicken and 2 a Bealnner'0 Star*=36ooIi develop the broader knowledge of the observer. These facts are stated in untechnical language, and they are intended to be suggestive rather than complete. In the hope, moreover, that the reader may be moved to seek elsewhere for fuller materials, the names of a few useful books — some elementary and some that are more technical — are added at the close. But sufficient information and guidance are given in the present volume to advance the beginner at the very opening of his study to a use of the simpler optical instruments, and to direct him at once to the more interesting telescopic objects. The Unaided Eyes Much can be done, and much known, without optical aid of any kind. The science was founded by men without telescopes. The Egyptians, Hebrews, and Arabs had none; Copernicus had none; Kepler, even, had none — or had none till after he had made all his larger contributions to astronomy. And yet an elementary knowledge of the familiar stars — knowledge easily within the grasp and interest of the average child of twelve — is wholly left out of the lives of multitudes of men and women largely because it is assumed that in order to know the stars they must have elaborate instruments. There are many who may well send up Carlyle's oft-quoted plaint: "Why did not somebody teach me the Constellations, and make me at home in the starry heavens which are always overhead and which I don't half -know to this day?" By reason of such ignorance the world is, I think, the poorer. For, after all, astronomy is not the most important thing, by any means, that the stars have to teach us. To know them is to know a world that is intrinsically beautiful, a world full of the immense and the illimitable — and yet not vague, inchoate, confused, but coherent, and of exquisite precision in the definiteness and consistency of its order. Really to dwell in such a world and to dwell in it intelligently and responsively is to be more completely "at home" within the universe in which we live, — for Carlyle's phrase is just. And if there be "no time" in our hurried and busy generation for a sense of the mystery and order of the stars, is not this itself one of the reasons why we should take time for them, and for the healing power of those silences to which they league their un- ceasing invitations? Our life, just now, is not too rich in imagination, nor too deeply moved by the sense of reverence or the touch of wonder. First of all, therefore, and as a basis for all that any optical instrument may contrib- ute, I have attempted in this little book to bring the reader to such a knowledge of the stars as may be acquired by the employment of the unaided eyes and the average mind. But both — the eyes and the mind — must be employed. Not that the task is at all exacting. Indeed I am familiar with no other class of useful and interesting information so quickly or readily acquired by the beginner. I am speaking, of course, not of technical astronomy but of the stars themselves — their groupings, their movement, their seasons, their individual characteristics. But eye and mind must be employed — not disemployed, as is too often the habit of those who flit vaguely and absently from topic to topic among the various fads of the "nature-lovers' " cult, — really seeking anything but nature and loving nothing but the vague sense of being "broad." Yet fifteen minutes of real reading by day, and (even more important) fifteen minutes of attentive looking at the actual sky by night, will shortly put the real clues of the subject into the hands of any interested learner over the age of twelve. Yotmg people who know their way about the skies as familiarly as they know their way to the post-office are not more remarkable mentally than those who do not ; they are as real as the boy who can easily quote the batting averages of his favorites ®ur Iberitage in tbe Stars 3 in cricket or base-ball, or the woman who can quote the prices on the fur coats in the ten shops just visited, or the man who has no trouble remembering "quotations" on 'change. It is merely a question of being interested. Opera-Glass and Field-Glass In learning to identify the star-groups, or constellations, an opera-glass is always useful. While not essential, such an instrument is of value partly because it adds greater brilliancy to some of the richer star fields, and partly because it wiU often aid the beginner in locating the fainter stars and in more readily tracing the outlines of the constellation figures. This is especially true on misty nights. On nights distinctly foggy, waiting is the better part of science. The stars will return again; and an optical instrument, from the least to the greatest, will not work many wonders in bad weather. The advantages of the opera-glass are possessed in even larger degree by the modem "field-glass," or prism binocular. Many of these, unfortunately, are almost as expensive as a telescope, but while lower than a telescope in magnifying power they are extremely convenient in size and their uses are more varied. Those who already possess such a glass will gain great pleasure from its use at night, and those who do not own either an opera-glass or a binocular will find on p. 97 some further instructions as to the selection and cost of instruments. We cannot say that their use, valuable as it is, is whoUy necessary to a pleasurable knowledge of the stars. StiU less can we say that the occasional use of optical help, however great, will ever serve as a substitute for the interested, intelligent use of the unaided eyes. Yet as we use our eyes, most of us wish to see better than we do; the use of an opera-glass soon makes us wish to use a field- glass or a "spy-glass"; and the use of these will soon suggest, at least in many cases, the larger possibilities of the telescope. The Small Telescope The impression that the really fascinating interests of astronomy are solely within the scope of large and expensive instruments is quite unfounded. All the characteristic subjects of observation are within the scope of simple and inexpensive glasses. It is true that op- tical aid, of some kind, is desirable. The almost inconceivable distances of space can be partly traversed by our unaided vision, but it is absurd to claim that without optical assistance of any kind we can see just as well as though we had a telescope. The glass need not be large. It may magnify but fifteen times or twenty times or sixty. But in each case there is a gain. Indeed, with a glass magnifying only two times the object is brought twice as near. With a glass possessing a magnifying power of twenty or a hundred the object is brought nearer by twenty or a hundred times, and, if there be sufficient aperture, is made to appear proportionately brighter or clearer to the average eye. So wide, however, are the reaches of the universe that even such changes do not always endow our objects of vision with impressive "size." The largest subjects take on dimen- sions that to the beginner seem of very meagre bulk. Yet the real telescope, however small, will show — as I have said — the characteristic objects of astronomic interest. It may not show all the star-clusters, but it will show enough to illustrate charmingly just what a star-cluster is. The small instrument will not show all the double stars or all the 4 a Beginner's Star^Boof? conformations upon the surface of the moon; but to the real observer it will reveal stars of varying colors — double, triple, and quadruple; and it will make the face of our moon a spectacle of increasing fascination. Its larger mountains, "seas," and "craters," indeed more than two hundred features of its topography, stand out in clear relief. Ob- jects such as these, together with the crescent phase of Venus and the four larger satellites of Jupiter are easily within the scope of a 2 -inch* instrument; and a telescope of 23^, 23^, or 3 inches will show these objects — and many others — under still better conditions of light and power. The photograph of the double cluster in Perseus shown on the opposite page was taken with a large instrument ; but the existence of the cluster may be detected with an opera-glass, and much of its beauty and impressiveness may be caught with even the smallest of telescopes. At a cost of from $20 to $150, according to size, quality, and equipment, the average man or woman can command an instrument that will open a new world of abundant and varied interest. The Sky and its Maps I once asked an accomplished watcher of the skies how he had managed to begin, and to begin successfully. His reply was — "I had a friend." There could have been no better answer. There is, indeed, no better help toward learning to recognize the stars and the star- groups of the sky than the friend who knows and who is able and willing to teach. But such a friend is not always present ; and it sometimes happens that such a friend, even when present, will crowd so much into his occasional opportunities for instruction that the re- sulting impression, to the beginner, is bewildering rather than informing. In any case, .and however deliberate the instruction, a chart or map is always helpful; and such an aid is especially important if no friend be right at hand. Here, however, we meet one of the real difficulties. The vault of the sky does not appear to us as a flat sur- face but as "an inverted bowl." Our earth seems to us to revolve on its axis at the centre of a hollow sphere, lighted from the sun by day and from the moon and the stars by night. As we look away to the horizon, whether toward the north or east or west or south, we seem to be gazing not at a fiat wall but at concave impalpable surfaces which, bending inward, meet at the zenith overhead. Now if these northern or western or eastern or southern skies were flat, it would be a simple matter to map them precisely as they are. But just because these surfaces are not fiat but like parts of the inner surface of a hollow sphere, we cannot draw or print them on a fiat surface without causing a certain amount of distortion in the picture. This distortion is not great at the centre of the map, but at the edges we must always remember to allow for it in comparing the map with the actual sky. In order to reduce this dis- tortion as far as possible I have here abandoned the attempt to present the whole sky in a single map. Two maps are given for each "sky," one showing the stars as the observer faces directly north, one as the observer faces south. But where, at the edges of the maps, distortion does appear, it has seemed best to face it frankly ; — not to ignore it or conceal it but to deal with it as inevitable, to point it out, and to show — so far as possible — how we may allow for it and correct it. * Telescopes are usually classified, as to size, according to the surface diameter of the lens at the large end of the instrument. A 2-inch telescope, and a 3-inch, are telescopes in which these lenses are, respectively, 2 inches or -i inches in diameter. A 2-inch will bear a magnifying power, for the average eye, of from 15 to 70 diameters; a 3-inch from 25 to 1 10 diameters. These are low estimates. The trained eye can of course utilize far higher magnifications See, for further practical suggestions, pp. 104, no. REGION OF THE DOUBLE STAR CLUSTER (/l, x) IN PERSEUS From a photograph tatten at the Yerkes Observatory 5 6 H Beginner's Star^Booft In at least one other respect the system of mapping here adopted will be of special service. The reader is provided not only with a series of Key-Maps on the right-hand pages, but also with a series of Night-Charts, on the left hand, showing the actual sky, without lines or symbols. The observer is thus enabled while looking at the pages of his book, to enter more easily into the mental experience of relating the night sky to a printed map. This — even where there may be some distortion — is a more important privilege than the veteran star-gazer has always realized. Usually, the beginner must look at a map in a book, a map somewhat crowded with lines and symbols, and then go look at the sky. The sky to which he turns has on it, how- ever, no lines, no letters, no symbols. Just because the beginner is a beginner, the mental experience of relating lines, letters, and symbols to a real sky (and a dark sky at that) which has on it no such markings, is wholly new. The task is likely to seem even more difficult than it is ; and it often proves discouraging. Through the use of the Night-Charts here provided, the beginner easily learns, from the Key-Map opposite, how to associate the lines and symbols with the uncharted sky. He can enter into this new mental ex- perience by easy, deliberate stages and at his own convenience. Having first "done it in a book," it will be much easier to do it afterward in the open. And in using the book it will often prove interesting to cover the Key-Map with a card, and test, by first looking at the Night-Charts alone, just how much of one's star-lore has been remembered. The same general method has been followed with the moon. On the left-hand pages are photographic reproductions of the actual moon, on the right-hand pages — drawn to the same scale — are the numbered Key-Maps. Because the stars repeat themselves, there will be much repetition in the text. Because intended primarily for the beginner, these repetitions must extend not only to the objects of observation but to methods. The repetition of elementary facts and suggestions may prove an irritation to the fastidious, but as the volume is intended for iise rather than as a book merely to be read, there seems to be no alternative. The beginner may at first think that the Night-Charts and their Key-Maps are rather full, presenting too many stars and too much detail. They are not fuller, however, than the sky. Some books upon the subject do present only one star-group at a time ; and some — while presenting all the area of the sky — ^reduce the number of objects in the picture by omitting most of the smaller stars. But if we present the sky at all it is best, perhaps, to present it just as it is or as nearly so as we may. A few of the smaller stars have been omitted, but should we leave out all of the smaller stars we should often have to omit some of the most characteristic features of a group ; and in presenting only one group at a time we should have to omit one of the most interesting phases of the subject — the relation of the groups to one another. Two additional reasons have seemed to me important: I have wished to make the volume not only a good book with which to begin, but, as already suggested, I have tried to make it also a book with which to go on. Not that the advanced observer will care to stop short of manuals larger and more technical; their use will be both interesting and neces- sary. And yet the simpler book, if sound in method, should not be so simple as to be outgrown before the aid of more pretentious manuals can possibly be utilized. Secondly, the detail of the maps has seemed to me to be justified by the needs of the telescopist. It has always seemed to me absurd to declare that the intelligent beginner must postpone the pleasure of using a small instrument till he has mastered the constellations. The telescope would be used far more largely both in our schools and in private hands if the beginner could quickly learn where the objects of interest may be found, and how to point ®ur Iberitage in tbe Stars 7 the instrument under the guidance of clear maps directly related to the actual sky. Such needs, and others of like nature, the drawings of this little volume are intended to meet. By placing the general descriptions of the star-groups directly under the Night-Charts on the left, and the descriptions of telescopic objects directly under the Key-Maps on the right, we are able to introduce the amateur very early in his study both to a knowledge of the constellations and to the direct use of the telescope. It is not unlikely, however, that the maps will seem, at the first, unduly crowded — in spite of what has just been said. The skies themselves are full of variety and detail; the subject — to the beginner — is new, its vocabulary unfamiliar, its symbols strange. What wonder, therefore, that he cannot "lazy himself into it" as he might lazy himself into a new game. But the subject is not difficult. Its possibilities are quickly available. Its rewards are not delayed. They come with the first steps, and with succeeding steps are richly multiplied. One suggestion, however, should be kept in mind: "Proceed slowly, at the first." Do not attempt too much at once. Get clear strong grasp on what you do learn. Take one thing at a time. In such case, each item of progress may be made a secure basis of association ; group may be added to group, fact to fact, till suddenly — as one learner, in delighted amazement, expressed it — "the constellations will seem to walk down to you out of the sky." Your landscape here upon our earth may change with each mile of your joumeyings. Your skies, however, will remain. Whether in San Francisco or New York, whether in London or Florence, the same skies, approximately, will arch themselves over you, and spread above you "the loved familiar roof of home." They will unite you with past ages and older cultures, whether Biblical, Oriental, Greek, or Roman, just as they unite you to the lands of the present. And while they touch the larger emotions and open broader horizons to the mind, the imagination to which they speak is not that vague illusion of the inchoate which a superficial hour so often confuses with the splendor of the sublime, but the imagination which springs from the evidences of precision and exactitude, from the sense of method and the bracing consciousness of law. It is a wholesome world in which to think and dwell. "Plainness and clearness without shadow of stain! Clearness divine! Ye heavens, whose pure dark regions have no sign Of languor, though so calm, and, though so great, Are yet untroubled and unpassionate; Who, though so noble, share in the world's toil, And, though so task'd, keep free from dust and soil! I will not say that your mild deeps retain A tinge, it may be, of their silent pain Who have long'd deeply once, and long'd in vain — But I will rather say that you remain A world above man's head, to let him see How boundless might his soul's horizons be. How vast, yet of what clear transparency! How it were good to abide there, and breathe free; How fair a lot to fill Is left to each man still!" Matthew Arnold: A Summer Night. NEBULA IN CYGNUS, KNOWN AS N. G. C. 6992 From a photograph taken at the Yerkes Observatory nil. ©bjects to l)c Seen: ZTbe Stellar TKHorlb What Are the Stars? One will often note in some current "Almanac" the statement that Venus or Mars or Saturn or Jupiter is the evening or morning "star." The expression, however familiar, has led to much misunderstanding. In the strict sense, Venus, Mars, Jupiter, Saturn, Mercury, are not stars at all. They do not shine by their own light. They are planets, as is our Earth also, shining by the reflected light of the Sun. About the Sun, these, together with " the other planets, Uranus and Neptune, revolve ; and they are — with their attendant moons — the most important factors in what is called the Solar System, i.e., the system of the Sun, or the system having the Sun as centre. The stars, in the stricter sense, lie far outside this system. Let us note for a moment the comparative distance from our Earth of the very outermost of the known planets and the very nearest star. The planet at the greatest distance from the sun, and from the Earth also, is Neptune, larger than our globe, but so far away as to be invisible to the naked eye. Neptune is 2792 millions of miles away. That seems, indeed; a vast distance. Yet the very nearest of the stars proper is more than 8000 times as far, is distant — in fact — more than 25 millions of millions of miles. If, therefore, some of the stars seem small to us as they "twinkle" in our night skies, it is only because they are so very far away. And if some of them seem large and bright, it is not necessarily because they are very near. It is because, although at vast distances from our earth and from our whole solar system, they are so immensely great in size. Most of the brilliant stars are actually nearer, than the fainter, but Deneb, — one of the brighter stars in our sky — is also one of the more remote. Nor is Deneb unique. Most of the stars are indeed superbly large and. brilliant — many of them being far larger and brighter than our sun. For our sun itself is a star (strictly, of course, our nearest star), and all the stars are suns — suns set so inconceivably far away in space that in many instances their radiance comes to us only as a trembling point of light. We have thus answered the question. What are the stars? We know them to be suns, suns shining by the intensity of their heat. Star Distances So far away are the fixed stars that the mile as a unit of measurement becomes almost meaningless. Astronomers have therefore sought a longer "yard-stick" and have taken for this purpose the distance travelled by light — speeding at a velocity of 186,324 miles a second or over 11 million miles a minute — -in a year of time. This unit of measure, or "yard-stick" of the universe, is called the light-year. The nearest of the fixed stars thus far measured is Alpha (a) in Centaurus, not visible from our northern latitudes. This star is 4.3 Hght-years distant. The nearest of all the bright stars visible in Europe and North America is Sirius, 8.7 light-years distant. In other words, the light from Sinus which reaches our eyes to-night started on its way more than 8 years ago. Or, to state lo H Beginner'6 Star^BooFi the same fact somewhat differently, should Sirius be blotted out to-night, we should know nothing of it for more than 8 years. A table giving the latest measures for about 50 of the important stars will be found on p. 139. Star Magnitudes and Star Symbols Because some, at least, of the fainter stars are nearer than some of the bright ones, and because some of the bright ones are farther from us than many of the faint ones, we do not attempt to classify the "magnitudes" of the stars according to their actual size. We base our classifications of magnitude not on the size or nearness of the star in itself, but on the relative brightness of the star as viewed from our earth. So careful and exact has been the work of astronomers, that every star that our eyes can see, without a tele- scope, is; not only registered in well-known catalogues and star-maps, but each star has assigned to it a specific magnitude based on actual observations made with instruments of high precision.* Of these, six different magnitudes, or degrees of brightness, are recognized. A sixth- magnitude star is barely visible with the unaided eye, even under good atmospheric con- ditions; a fifth-magnitude star is a little brighter, and so on till we reach the brightest — the stars of the first magnitude. A few of the stars, however, are so very much brighter than the average first-magnitude star that decimals of unity, figtu-es lower than i, have been called into use. The star Sirius, indeed, is classified as of magnitude — 1.6, which means that it is over ten times as bright as a star of precisely the first magnitude ; nevertheless Sirius is listed, in a general way, among the stars of the first magnitude. It is thus always important for the. beginner to remember that the smaller the numeral of classification the brighter the star, and vice versa. Of first-magnitude stars there are twenty ; a Hst of them will be found on p. 140. The making of so brief a Hst as that on p. 140 will not seem to the beginner to present many difiiculties, but that all of the stars of the six larger magnitudes should be accu- rately listed and classified will seem almost incredible. Their number, as we look upward on any clear and cloudless night, will at first seem fairly limitless. Yet, including all of the first six magnitudes, thore are really only about 5000 such stars — stars visible to the unaided eye — in the total sphere of the heavens. As we see only half this number at once (for naturally we cannot survey the skies beneath our feet), the number visible at any one time must be reduced to about 2500. When we realize moreover — as has often been pointed out — that those near to the horizon are largely obscured to us by mists, trees, houses, etc., it is evident that the number actually before us at any given hour is even smaller. Newcomb puts the total at from 1500 to 2000. The use of a telescope will, of course, bring multitudes of others into view. Even so small a number as 2000 will doubtless seem, at first, to be so bewildering as to make any definite knowledge of the sky altogether impossible save to an observer with special gifts of mind or training. But this is by no means the case. If the stars greatly changed their position from night to night, confusion would be inevitable. But, though making their apparent revolution once each 24 hours, their places in relation to each other have been practically unaltered for unmeasured centuries. As we watch them, we quickly leam mentally to group the fainter ones about the brighter, according to outlines or figures * The two most important catalogues of the stars by magnitudes are that made by the Royal Observatory at Pots- dam, Germany, and that made by the Observatory of Harvard University, U. S. A. A list of the 70 brightest stars is printed on p. 140, showing their relative magnitudes. Z\)e Stellar MorlD n that have descended to us from the past. Some of these traditional groupings seem to us illogical, but inasmuch as an attempt to change them (and to sectu-e agreement as to the change) would only increase confusion, they have been retained. SPIRAL NEBULA, KNOWN AS MESSIER 51 From a photograph taken at the Yerkes Observatory In one respect, however, a change has already come. The ancient world saw in these groups of stars the figures of birds or animals or mythological heroes. These fancies served, for many centuries, a useful purpose. It was possible to designate the location of a star, for example, by reference to it as the brightest star in the head of the Dragon, or in the left foot of Andromeda, or in the head of Taurus, the Bull. But this method 12 a Beginner's Star^Booh was necessarily crude, and never very accurate. In the seventeenth century (1603), a German astronomer named Bayer published a series of star-maps in which most of the brighter stars in each group were designated by letters of the Greek alphabet.* Roman letters came also to be employed, as well as our ordinary Arabic figures, i, 2, 3, etc., so that these shorter and easier symbols have gradually passed into universal usage. For readers of this book who may be unfamiliar with the Greek characters I have ventured to simplify in two ways the using of these symbols. First the whole Greek alphabet, with the names of the letters, is printed on p. 33". As many, however, will not wish to trouble themselves to memorize the alphabet as a whole, I have also given in the text itself the English names of the Greek letters wherever used — ^for example, the Beta (/8) of Perseus; the Gamma (y) of Andromeda, etc.f Thus, the beginner who has no knowledge of Greek will not only be able to follow the notes below the maps in their references to the stars, but will soon gain — almost without knowing it — a working knowledge of the Greek symbols. The old mythological names for the star-groups or constellations are stiU retained. So also we still keep the ancient names for many of the individual stars. But the figures and shapes of heroes, etc., are usually so difficult to discern, so many are now quite un- certain in outline and without real helpfulness to the beginner, that they are falling more and more into disuse. In this book, while some of the more obvious are pointed out in the notes, I have frankly omitted them from the maps. Experience has convinced me that they are not of serious value in the learning of the constellations and that the effort to trace them sometimes withdraws attention from the interest of the stars themselves. For the stars themselves, in the light of our modem knowledge, possess an ever deeper intrinsic interest. The Double Stars With our earliest use of the telescope, however small, we shall find that we must add to the list of the 1500 or 2000 stars visible in our sky. Not only shall we see many stars not seen before, but stars noted quite clearly with the unaided eye will now be seen to be two instead of one. Castor, for example, one of the brightest stars in the constellation Gemini, is thus found to be a "double." Each of the components, if these could be set farther apart in the sky, would prove bright enough to be clearly seen without opera-glass or tele- scope. They are really so near together, that the two stupendous suns look to the unaided eye like one star. A magnifying power of 70 will show their separation. The com- panion orbs are in revolution about a common centre of gravity; and Castor is therefore called a Unary. We shall come upon other binaries as we take up the study of our maps. We shall find also that not only are some of the stars binary in character but that there are cases in which the components are so close together that no telescope will ever be able to divide them. The division has been detected by the spectroscope ; and these * The suggestion had first been made by the Italian, Alexander Piccolomini, in 1559. For all technical purposes astronomers now designate the positions of stars by right ascension and decUnation, the celestial equivalents of longitude and latitude, see note 14, p. 32. t In many text-books, and in the technical literature of astronomy, the references to individual stars are made merely by the use of the Greek letter in connection with the Latin genitive of the constellation name. For, example, the star Alpha (a) in Lyra, is thus written a Lyrae; Delta (5) in Orion, is written S Ononis etc. Knowing that there are many interested students of the stars to whom Latin and Greek forms are confusing I have not only included the Enghsh names of the Greek letters, but have used English prepositions for Latin genitives. We may thus simplify the course of the beginner without sacrifice of accuracy. See also p. 141. Ebe Stellar THaorlt) 13 stars are therefore called spectroscopic binaries; see p. 143. Castor — to which we have just referred— is really a quadruple object ; for each of the components visible in a small telescope is itself a spectroscopic binary. There are also triple stars, and quadruples, etc., as well as doubles. Some of these are apparently bound together in interdependent systems like the binaries, revolving about a common centre; some, upon the other hand, are merely "optical" doubles or "optical" triples, — stars not truly bound together, but placed in the same line of sight when viewed from our position on the earth. Their apparent nearness to one another is wholly deceptive. In other cases, however, the relative nearness of the components to each other is so evident, and their revolution about a common centre of gravity is so fully proven, that the observation of double stars is one of the most delightful interests of the possessor of a small telescope.* Some of these true doubles, as we shall see, are sufficiently "wide" to be divided by a field-glass. They become all the more interesting when we note that the separate components of the double or triple stars are, in many cases, of different colors. In the star marked Gamma (y) in Andromeda, for example, the larger component is a golden yellow, the smaller a delicate emerald. In that marked Alpha (a) in Hercules, the larger star is a light yellow, the smaller component a dark blue; and in other cases, also, the two components are of contrasted tints, yellow and white, yellow and green, orange and purple, white and gray, yellow and red. In some of the more striking cases the impressions of color are illusory, but there are also many cases of true color-distinction. Observers are often disagreed as to their impressions — as is often the case in our impressions of color in other objects — and there are instances in which the stars seem to have changed their colors, somewhat, since the earliest period of observation. The subject is accordingly full of interest and charm. In the calm, unhurried watching of a double star through a good instrument on a clear moonless night, one has the same exquisite pleasure as that awakened by the flash of two contrasted jewels, each enhancing the subtle thrill and radiance of the other. The smaller component, as it clings close within the light of the larger, will often look like a tiny dewdrop trembling within the splendor of some golden globe. The observer knows that he is really gazing upon two mighty suns at so great a distance from us that the imagination is utterly inadequate even to its elementary appreciation and that these close-bound stars revolve about their common centre probably divided by many hundreds of millions of our earthly miles. Yet a night which lies thus about us wearing suns for jewels never loses its appeal even for the hardened astronomer. The expressions of enthusiasm for the wonder of the stars, of deHght in their mystery and charm, have chiefly come in every age not from the "mere amateur " — as the cynic might suggest — but from Kant or Laplace, from Kepler, the Cassinis and the Herschels. The Variables In the Autumn of each year, through the hours of the early evening we shall find at the northeast (or in Spring at the northwest) the star known to the Arabs as "Algol." In maps of the stars it is usually marked as Beta (fd) in the constellation Perseus. (See Key-Maps on pp. 47 and 59). Algol shines usually as a star of the second magni- * Speaking of Tennyson's remarkable knowledge of the stars and of the accuracy of his poetic references to scien- tific matters, Sir Norman Lockyer says: "I visited Tennyson at Aldworth [his home] in 1890 when in his 82d year. One of the nights during my stay was very fine, and he said to me, '.Now, Lockyer, let us look at the double stars again,' and we did. There was a two-inch telescope at Aldworth. His interest in astronomy was persistent until his death." Tennyson as Student and Poet of Nature, by Sir Norman Lockyer and Winifred L. Lockyer, London, 1910. 14 a IBcQlnnct's Stars'Booft tude. At regular intervals, however, — and these intervals are so regular that they may- be predicted to the fraction of a minute, — ^its light begins to fail. Within 4K hours it loses more than half its brilliance. It stays at "minimum," its point of faintest bril- liancy, for 20 minutes; and then, in approximately 3^/2 hours its light again increases until it once more reaches the brightness of a second-magnitude star. After remaining at .its greatest brilliancy for 2)^ days, its decline begins anew. There are known at present more than 1000* variable stars, although the stars of the Algol type are only about 80 in number. Most of the variables are too small, however, to be seen with the unassisted eye ; but some of the brighter of these stars are easily observed without optical aid of any kind. The true explanation of the variations in Algol was suggested as early as the i8th century, but no final proof of its validity was afforded till the more recent researches of Vogel, Pickering, and Chandler. The chief point of interest to the beginner is that Algol is attended by a dark companion, the two bodies being in revolution about a common centre of gravity or about another body invisible with our instruments. As Algol passes behind its dark companion, the dark companion is interposed between Algol and our earth. Thus the brighter star is eclipsed by the dark one, and this eclipse corresponds to Algol's period of lowest brilliancy. As the revolution proceeds, the brighter star passes from the shadow of eclipse, and its normal brilliancy returns. The star known as Mira — marked Omicron (o) — in the constellation Cetus (Key- Maps pp. 61, 41) is quite different in type. Its period of change is much longer — sometimes 10 months, sometimes 11. It is usually invisible to the naked eye, but at intervals of a little less than a year it becomes sufficiently bright to be recognized, gradually increasing in brilliancy till it reaches its maximum, and then, within less than 3 months, sinking again so low as to be wholly invisible except in a telescope. Its precise degrees of brilliance, both at its faintest and at its brightest, are as irregular as its periods. At its maximum it shines sometimes as a star of almost the first magnitude, but more fre- quently as of the second or third. At its minimum it falls to magnitude eighth or ninth or tenth. Unlike the case of Algol, no adequate explanation of the variations of Mira has as yet been found. There are several other types of interesting variables each having many representatives, but for these I must refer the reader to the more general text-books on astronomy, noted on p. 144. Mira reaches its greatest brilliancy at intervals of 10 or il months, — for 1911 in July; for 1912 in June; for 1913 in May, etc. Star Colors and Star Character We have already fovmd, in connection with the double and multiple stars of the sky, that the components of such bodies are often different not only in size but in color. A little careful attention, however, will show us that color is a characteristic of all the stars, whether double or single. At a first view on a clear, moonless night, all may seem alike; but closer observation will show that while some are white, some also are yellow, others are a deep orange, others red. Says Sir Norman Lockyer: "The stars shine out with vari- ously colored lights. Thus we have scarlet stars, red stars, blue and green stars, and indeed stars so diversified in hue that observers attempt in vain to define them, so completely do they shade into one another. Among large stars, Aldebaran, Antares, and Betelgeuze are unmistakably tinged with red ; Sirius, Vega, and Spica are of a bluish white ; Arcturus and Capella show a yellow hue like that of our sun. If we include those comprised within star clusters, and not classified individually, the total would be nearer 4000. Additional variables are discovered each year. SPIRAL NEBULA IN COMA BERENICES, KNOWN AS H. V. From a photograph taken at the Mt. Wilson Solar Observatory 15 1 6 a Beginner's Star^Booh "In double and multiple stars, however, we meet with the most striking colors and contrasts ; Iota (z) in Cancer, and Gamma (y) in Andromeda, may be instanced. In Eta (77) of Cassiopeia we find a large white star with a rich ruddy purple companion. Some stars occur of a red color, almost as deep as that of blood. What wondrous coloring must be met with in the planets lit up by these glorious suns, especially in those belonging to the compound systems, one sun setting, say, in clearest green, another rising in purple or yellow or crimson; at times two suns at once mingling their variously colored beams! A remarkable group in the Southern Cross produced on Sir John Herschel ' the effect of a superb piece of fancy jewelry.' It is composed of over lOO stars, seven of which only exceed the tenth magnitude; among these, two are red, two green, three pale green, and one greenish blue." Impressions quite so striking are not within the range of the unaided eye, nor even within range of the instruments available to the average amateur, but the varied beauty of the familiar star colors as seen in ordinary telescopes will find increasing appreciation as knowledge grows and as mind and eye become more practised in the art of acctuate dis- crimination. As we have already seen, there is much authority for the contention that colors other than the various degrees of white, yellow, and red are due to optical illusion; but, where — as here — these "illusions" are permanent factors in our scene, even as viewed by the best eyes and the best instruments, they remain for the practical observer as legiti- mate impressions. The questions as to how these illusions arise, and as to how they may be said to differ from the admitted hues of white, yellow, and red, only add to the interest of the subject. A star, moreover, is not a timid flame lighted in a chimney comer. We have seen that among all the stars visible to the unaided eye from the latitudes of Europe or North America, Sirius is the nearest. And of all the fixed stars of the sky it is the brightest. Yet as its very light, at a velocity of over 186,000 miles a second, takes more than 83^ years in which to reach us, we are not surprised to learn that it is more than 20 times as luminous as the sun. The star Rigel, shining at the lower right-hand comer of Orion, see pp. 41 , 45, seems not quite so bright. Is it therefore a smaller sun? On the contrary, its real luminosity exceeds that of the sun by 8000 times. Why then should Sirius seem the brighter? Chiefly because Rigel's distance from us is so vast that the light from it which meets the eye to-night started on its long journey more than 450 years ago, or before the birth of Shakespeare.* Betelgeuze, the other first-magnitude star in Orion, is not so bright nor so far away — being at a light distance of about 100 years — but, upon the other hand, its mass has been conservatively estimated! at more than 22,000 times the mass of the sun. Bodies so huge in their proportions and so splendid in the energy of their effulgence are not easily to be described, either as to their constitution or their color, by a simple label. As to each star, the prevaiKng color may be red like Betelgeuze or yellow like our sun, but as we watch it closely we are likely to see the torrential flash and inter- play of more varied hues. Such is especially the case with Sirius; so is it also with Rigel and Vega and Capella. Indeed, as to the factor of color, we may well say that each star is of many stars compounded. And yet each has its own general hue, for each is itself and not another. Each one of these far off suns, as we come to know it, and to consider not its color alone but the factors of magnitude, of motion, of distance, — its place in the sky, its relation to *Kapteyn accepts the almost insensible parallax of Gill and Finlay (o."oo7), undoubtedly the most accurate thus far obtained. See the table of parallaxes and star-distances, p. 139. t Problems in Astrophysics, by A. M. Gierke. A. & G. Black, London, 1903. Cbe Stellar iKHorlb 17 other stars, the seasons of its rising and setting, — will be found to possess an individuality of its own. We soon come to know it and to count upon its friendly shining. Even though we may not always be familiar with the varied facts or discoveries concerning it, its identity will become, in instinctive ways, familiar. It is said that an old tailor when testifying in court was once questioned as to certain stitches in a coat. "They are my stitches," said the tailor. "How," asked the judge, "do you know they are your stitches? Are they longer than the stitches of others?" — "No, your honor." — "Are they shorter?" — "No, sir." " Then how," exclaimed the judge, "can you claim that they are yours? " " Do you think, your honor, ' ' replied the tailor, ' ' that I do not know my stitches ? ' ' And the testimony stood. How seldom, indeed, can we give particulars as to friends that we have known. Was the hair dark or blond? Were the eyes blue or gray or brown? Was the mouth small or large? We cannot always say. But when we see the face, its identity is clear; we know it. How often, watching at dusk when the fainter stars are hid, and looking out to the horizon, we see a flash of slender light just at the brow of some far ofif hUl or down an opening lane through a neighboring wood, — a star returning at twilight, after a long absence. At the moment we may not know it, but at a second look the mind leaps in recognition — it is Regulus, or Capella, or Vega, or Antares ; old associations throng within us ; memories of other recognitions, of congenial spirits who with us once watched its rising; of changes that have come ; of changes that have not come, but that still wait the will and the labors of men. Thus is it that the return of the stars may be as the greeting of old friends. Star Clusters and Nebula While the stars, therefore, possess an individual identity, there are instances in which we can know them only in masses or clusters. Just as men and women, however distinct they may be in their own personalities, will often seem from the standpoint of a spectator to "lose themselves in a crowd," so is it with the stars. At certain points in the sky we find them gathered so close together that it becomes impracticable to try to distinguish them from one another. These dense masses of stars are called "clusters." Some of these are visible only in a telescope, though the telescope need not, in all cases, be a very large one. Two of the most beautiful, however, are visible to the unaided eye ; and here, at least, not all the larger stars are lost in the mass ; — some of them shine out with marked individuality. One of these clusters is called the Pleiades and one the Hyades; both are in the constellation Taurus, the Bull. In our notes upon the maps (see pp. 40, 46, 58) we will indicate their position more precisely. The Pleiades* begin to appear at the northeast in our evening skies (8 P. M.) about October ist; and as the stars rise each evening about 4 minutes earlier than on the evening before, we shall see them each night at 8 p. M. a little farther advanced upon their way. In January, at the same hour, we shall find them, accordingly, too high overhead for con- , venient observation; but by April 1st, we shall again find them conveniently placed for observation at the northwest. As the stars make the complete circle of their apparent revolution once in every twenty-four hours, we can anticipate this yearly march through the months — ^if we desire — by "watching out the night." The sun's shining will of course make them invisible by day, but we may be quite sure that the Pleiades are actually in * " Many a night from yonder ivied casement, ere I went to rest. Did I look on great Orion, sloping slowly to the west. Many a night I saw the Pleiads, rising thro' the mellow shade, Glitter like a swarm of fireflies tangled in a silver braid." Tennyson: Locksley Hall. 1 8 a Beainner's Star^^HBooft our sky— at all seasons of the year— about i6 hours out of every 24. The watching of such a group for a few nights, not out of a window but under the actual sky, will, m itself, LARGER STARS IN CLUSTER OF THE PLEIADES {For view at culmination, the side to reader's right should he held downward^ From a photograph taken at the Yerkes Observatory prove a good beginning in astronomy and will do more to make clear the apparent motion of the stars than any amount of theoretic description. (See also pp. 22 and 24.) I say Cbe Stellar Morib 19 "apparent" motion, because of course the movement of the stars, in the sense in which I have here employed the word, is not real. It is our earth that really moves. Let us assume that about October ist we are looking at the northeast (nearer east than north) , and that at 8 p. M. we discern the five or six brighter stars of the Pleiades just rising above the horizon; at 9 p. M. they will be higher still. Indeed, if the horizon is shut off by high woods or tall buildings, or by clouds or fog, we may have to wait till 10 p. M. before we can get a good look at them. At corresponding hours on November ist or Decem- ber 1st they are, of course, higher up. See also, p. 134. To the average eye, under fair conditions, five or six stars in the Pleiades can be seen: under especially good conditions, seven. An abnormally good eye can see from eight to ten. With the use of an opera-glass — the average opera-glass magnifies about 3 diameters — as many as twenty can usually be counted. The use of a modem prism binocular, magnifying from 7 to 10 diameters, will reveal more than fifty; a small telescope will add many more ; a large telescope will add almost a thousand ; and, finally, the camera will bring the total to nearly 2500 — for, inasmuch as the photographic plate is more sensitive than any eye, the camera when adjusted to the telescope will reveal many stars that are beyond the reach of any instrument employed without photographic aid. No instrument gives a more beautiful representation of such a cluster than the small telescope with a low-power eye-piece. The use of low magnifying powers in the observation of clusters and nebulas is essen- tial, as will be more fully set forth hereafter. Other clusters will be indicated in direct connection with the maps. The location of the double cluster in Perseus, of the "Bee-hive" in Cancer, and of several others — if the night be moonless and very clear — ■ can be made without optical help, but there can be little appreciation of their real beauty without the aid of a field-glass, or a small telescope ; though even an opera-glass — especially when brought to bear on some of the coarser groups — is no mean assistance. We may say, indeed, that the whole Galaxy or "Milky Way" is in one sense a cluster. Spanning the sky "as a beautiful belt of pale light" it makes — when the moon is not shining — one of the most marvellous fascinations of a summer evening. Turning an opera-glass or field-glass upon it, we discover that it is not a mere waste of glowing cloud but that it is composed of thousands upon thousands of stars — stars that seem small because of their great distance from us, but which are, in many cases, far larger than our sun. The telescope, as we shall see in our study of our Key-Maps, will show that certain sections of it are peculiarly beautiful and impressive. The nebula is sometimes found in connection with the star cluster, as in the Pleiades themselves, but it is often found apart, and it is not strictly star-like in composition. Even when associated with such a cluster as the Pleiades the nebulous matter may be very faint — beyond the reach of average telescopes — and yet the stars which it enfolds may be large and bright. To use an imperfect illustration afforded by other conditions, we may say that a nebula looks as though it might be a tiny isolated patch of the Milky Way, but in its structure and composition it is gaseous. Sometimes this filmy mass is oval, some- times quite irregular, in form; sometimes it will seem to throw out wisps and streamers of effulgence, or, again, as shown in the illustration on p. 8, it will seem to us like the long and shelving undulations of a thin cataract of light, as it slips from star to star in its shining fall through space. Some of the most remarkable nebulae are spiral in form, and their luminous gases seem charged with star-like condensations, though no telescope — however great — has ever resolved these points of condensation into true stars. Some astronomers regard the 20 H JBeginner's Star^Booft nebulas as stars in process of formation, others regard them as stars in process of dis- integration. In certain cases the nebulas seem to be involved in a vast whirlpool THE GREAT. NEBULA IN ANDROMEDA, MESSIER 3t From a pholografk taken at the Yerkes Observatory motion, throwing off their streams of light and matter as a whirlpool in a flood seems to throw off its frothing waters from its centre. But so great is their distance from JLbe Stellar morlb 21 US or so inconceivable their magnitude that we have caught as yet no visual evidence of change. The nebulae, however, are not brilliant objects in small instruments. They are dis- appointing except to those fortunate enough to command facilities far beyond the range of the average purse. And yet it is of interest to get such glimpses of them as we may, even if we may not be able to command an impressive view of them. For even the highest optical aid can do little more than afford a suggestion of the facts. The longer diameter of the great nebula of Andromeda is more than 500,000 times the distance which divides our Sun from the Earth; p. 118; and light, speeding from end to end of this mass THE GREAT NEBULA IN ORION From a pholograph taken at the Yerkes Observatory at more than 186,000 miles a second, must take eight years in which to complete the jour- ney. The mere observation of such an object is worth while, however inadequate our view of it; and something of the beauty of at least one of these mysteries of the sky — the great nebula of Orion — is, as we shall see, within the range of our smaller instruments: "a single misty star, Which is the second in a line of stars That seem a sword beneath a belt of three. I never gazed upon it but I dreamt Of some vast charm concluded in that star To make fame nothing." Tennyson: Merlin and Vivien. Him. XearnitiQ to ©bserve: jfour 1ke^*(5roup0 Before taking up the larger maps the beginner will find it helpful to study the simple outlines of two or three of the smaller groups. The stars that I have chosen are not in all cases complete constellations but conspicuous groups that are easily and quickly identi- fied. By first learning to distinguish these, the task of learning to identify other groups is made easier and simpler. These key-groups become "guide-posts." They also serve another and more important purpose. Drawing them — as we shall try to do — in closer relation to our actual horizon than is possible with the larger maps, we can perhaps see more clearly just how these star-groups look, not only at their highest apparent altitude, but when they are rising and setting. With the star-groups toward the north, in the neighborhood of the pole, the problem of life-like drawing is quite simple. First of all, therefore, let us take the familiar "Dipper," — sometimes, in England and Canada, called the "Plough." Looking North — All Seasons The seven stars which form the "Great Dipper" are always in our northern sky. That we do not see them by day is wholly due to the fact that the daylight hides them.* The Sun is so much brighter than any of the stars that, whenever its light is in our sky, the stars are blotted out. But toward the day's close — if the air is clear — we can begin to see the brighter stars, and as the night comes on we find that the stars have been above us and about us all the while. As we watch them we soon see that they, like the Sun, seem to move from east to west; taking about 24 hours to complete their round. This — as in the case of the Sun — is, however, only an apparent motion. And there is another apparent motion of the stars, — that which brings us the star-changes of the seasons. In each case, that which really moves is, of course, the earth. One of these movements is that of the earth through its orbit round the sun ; the other movement — on which we here dwell — is the earth's rotation on its axis. We know that as we sit in our car in a railway station it will sometimes seem to move when that which moves is not our train at all, but the train just outside. So as our earth turns on its axis once in each twenty-four hours the stars themselves do not revolve, but they do seem to revolve within this period of time. The axis on which they seem to turn . will thus coincide, of course, with the axis of the earth — except that this axis will be longer, and its ends will seem to extend outward through the stars to north and south. Just as the north pole of the earth, for example, is the "top point" of the earth's axis (a point, Hke the centre of a wheel's hub, which seems not to revolve, but round which the earth turns) so is it with the apparent wheel of the stars. Its central * "Earth's dark forehead flings athwart the heavens Her shadow crown'd with stars — and yonder — out To northward — some that never set, but pass From sight and night to lose themselves in day." Tennyson: The Ancient Sage. Xearning to ©bserve 23 hub is thus at a point in the sky corresponding to the pole of the earth. If we can find this hub we may be sure that at this point there will be no motion of the starry sphere ; that round it the other stars will seem to turn; that as we come nearer to it their circles of revolution will grow smaller (just as the circles of revolution in a wheel grow smaller as we look closer to the hub) until, at the pole itself, there will seem to be no motion at all. This will all be clear to us as we watch the movement of the Great Dipper. Let us assume, for example, that on November 20th (a few days earlier or later will make little difference) at about 8 p. M. we are looking at the northern sky. At 8 p. M. on that date the Great Dipper will be found due north in the position marked A. You will see that it is low down, near the horizon, and that the stars marked Beta {ft) and Alpha {a) Polaris ^ The Pof9 Star •/ ^ ^^ A FOUR POSITIONS OF THE DIPPER are pointing upward toward a bright star located about midway between the horizon and the zenith (the zenith is the point directly overhead). This star is called "Polaris" or the Pole Star. If you will look northward again in a couple of hours you will see that the Dipper has moved. You will find it passing on its way from position A to position B. You will note, however, that no matter what its position, the stars a and ft are still pointing toward the Pole Star. You can see the Dipper advance from position A to position B in about 6 hours, if you care to maintain your watch so long. In six hours more you will find it very high up, at position C. It will then pass to position D, and thence to position A again. And you can see it pass through all these positions without sitting up any later, if you should prefer to look at it — through the course of the year — for a few minutes at about 8 o'clock each night. For on each night the stars complete their round just about four minutes earlier. They are, so to speak, always "four minutes fast." Each night at 8, therefore, after November 20th, the Dipper will be a little farther along than position A, so that at our chosen hour by February 20th the Dipper will be found not at position A but 24 H Beginner's Star»»Booft at position B. By May 20th, at about the same hour, we shall find it high overhead at po- sition C. At the same hour, on August 20th, we shall find it at position D ; and at about 8 p. M. on November 20th, we shall find that it has completed its circle and is once more at position A. All this will be made much clearer than it can ever be stated in a book if the beginner will take this simple diagram in his hands, turn to the north, and put real eyes on the real stars for one or two consecutive evenings. But, whether we really observe a Httle or read a Httle or do a Httle of both, there are four facts that will soon be quite clear. We shall note, first, that the stars are in apparent revolution about a central pole; secondly, that the stars in the Dipper marked Beta (^) and Alpha (a) — called the "Pointers" — are always pointing in the general direction of this pole; thirdly, that the star Polaris — alone among the stars — seems not to move; and fourthly, that the polar-point around which the stars revolve must therefore be at, or very near, this star. The fact is, of course, that the pole is not exactly at the star Polaris. Polaris, however, is so near to it that it may fairly be called the Pole Star and, if we could place ourselves precisely at our north pole, Polaris would seem to stand almost directly overhead, like a tiny celestial capstone to the projected axis of our earth. While, therefore, this star also revolves about the pole — the exact pole of the heavens being of course only an imaginary point — ^yet, because Polaris is so very near the pole, the circle which it makes, as it revolves, is quite small — so small that, for all ordinary purposes, the star seems to stand still. A star placed, however, a little farther from the polar-hub will, as the great wheel revolves, make a larger circle; and the farther from the pole we look — among our northward stars — the larger will be the circles of revolu- tion. Of the two Pointers, Beta (/S), of course, will mark a greater circle as it revolves than the star Alpha (a). And yet all the stars of our sky that are no farther from the polar-hub than the outermost star of the Dipper, can describe their circles of revolution without being carried below our horizon. They are always, therefore, in our northern skies. The stars, however, that are placed somewhat farther from the polar-hub will neces- sarily, as the wheel turns, dip below the horizon for a longer or shorter period; and the farther -they are from the pole the longer must they be below our horizon and absent from our skies. These stars, as our earth turns on its axis, will seem therefore to rise and set. Moreover, as we come to study them we shall see that our figure of speech must be changed. For as we face the north and look at Polaris we are gazing not strictly at the hub of a flat wheel, but — as we have said — toward the pole of a hollow sphere, its apparent axis the projection of the earth's axis, and its equator the projection of our own equator. We may therefore imagine the spokes of the revolving wheel — as they extend — gradually bending inward toward us, and forming the ribs of a vast including globe. We stand — inclosed as it were — at the sphere's centre. The circumpolar stars turn with the sphere itself, but as they lie so near the pole, the circle of their revolution never carries them out of sight. Sometimes, as we face the north, we find the Dipper above the Pole Star, sometimes below it; sometimes it is a little to our right, slowly cHmbing upward as in position B. Sometimes it is a little to our left, with the bowl turned downward as in position D, but it is always before us in our northern sky. Yet with the sphere's turning, the stars farther from the pole, like bright points fixed on the inner surface of its concave sides — as these arch themselves above and below the horizon — appear and disappear according to their hours and their seasons. Let us make this still clearer by turning to another of our key-groups. learniiiQ to ©bserve 25 Looking South — November to April We are now to look at a star-group quite far from the pole. So wide is the circle which it makes in its daily revolution that its stars not only dip below the horizon, but are really above it for only about lo hours in the 24. As it is so far from the pole we will face now towards the south. On the same evening, November 20th, let us first reaHze as we face southward that we have put the pole at our backs. The east, therefore, will be now at our left; the west will be at our right. At 8 P. M. on November 20th, the stars of Orion, perhaps the most beautiful of the constellations, begin to appear low down in the eastern sky. By 9 o'clock these stars will probably be clear of the mists that in Autumn so often Ke at "the edge of the world"; and by 9:30 or 10 they will be well placed for observation. This group is now, let us assume, at position A, with the three bright stars that pass diagonally through the great square, pointing upward ;* by i : 30 A. M. it will reach position B ; by 5 A. M. it will reach position C; by 8 A. m. it will have set. THREE POSITIONS OF ORION Most of US, however, do not care to watch through a whole night, even to foUow the march of such a constellation as Orion. We will prefer to follow the other method. Re- membering that the stars rise each evening four minutes earlier than on the evening before, we can just as well follow Orion through his march across the sky by looking for him through the hours of the early evening at successive dates. We shall need more time than one night or one week or one month. As Orion comes to position A four minutes earlier each night, so it will be four minutes earlier when he reaches position B ; and by 8 p. m. in January we shall find these stars nearer to B than to A. At 8 in February they will be quite at B, and by 8 p. m. in April they will be at C. We shall thus have almost six months in which we shall find Orion conveniently placed for observation among the stars of the early evening. This little diagram is placed at this point, however, not only in order that we may follow the course of one star-group, but in order that we may also get some idea as to how Orion looks as he rises and sets. The impression given in the diagram is not perfect. I have already explained that — inasmuch as the stars are not arranged on four straight * "Those three stars of the airy Giant's zone That glitter burnished by the frosty dark.'' Texnyson: The Princess. 26 a Bealnner'0 Star*=«ooft walls but seem to dot the inner surface of a hollow sphere — ^it is impossible to map them perfectly on a flat surface like the page of a book. But through such a diagram as we have just made, we can help to bring to ourselves a clearer picture of some of the positions of the star-groups that make the circles of their revolution far out from the pole. We can see how they slant, or tip, as they rise and set. If we attempted in our larger maps to show this slant or tip for every group we should have to make a globe. We could not do it well on paper without involving ourselves in more technical and practical difficulties than the beginner would care to try to understand. This slant or tip of some of the constellations is, on the other hand, very quickly under- stood in the light of a Httle actual observation. Moreover, many of the star-groups show little if any distortion in the maps; and as we look farther from the equator and nearer to the poles north or south we find it less conspicuous. Let us take, therefore, another group. It is Corvus, the Crow (or the Raven) ; and near it we will place the bright star Spica (pronounced Spl'-ka). if' \icA THREE POSITIONS OF CORVUS WITH SPICA Looking South — ^April to August Those who have seen the figures of beasts and birds in the star-groups of the sky have here found the Raven's eye and beak in the stars at the upper left-hand comer, the feet at the comer just below, the tail at the comer diagonally across from the beak, and a half- opened wing at the upper comer to the right. Others have drawn or imagined the Raven quite otherwise ; — for example, with the beak low down at the right as though picking up a grain of com. All such "pictures" are interesting or uninteresting — according to our moods. . Let us find our chief interest, however, in the stars themselves. The stars of this Uttle group are not especially bright, but the outline which they present is clear and simple. It will give us additional light on the lessons already suggested, and we may gain from it at least two other helpful points. Corvus rises at the southeast, shortly before the time when we find Orion setting at the west. On April 1st at 8 p. M. we shall find it a little above the horizon at the position marked A. If we follow it through its whole course in a single night, we shaU find that by II : 15 p. M., Corvus has advanced to position B and by 3 A. M. to position C, — setting about 4 A. M. Or, as we have already explained in relation to Orion, we can follow its march across the sky by keeping an occasional look-out for it, from week to week, in the skies of the early evening. While at 8 p. m. on April ist it will be found near position A, it may be observed — at the same hour — at position B on May 20th, and at position C by the 20th of July, unless the long daylight of July should then prevent our seeing it. You will note, however, how constantly the bright star Spica follows it — how closely, in fact, Spica is associated with it in all the positions through which it moves. You will learning to ©bserve 27 see, therefore, not only how Corvus helps us to find and identify Spica, but how Spica — one of the brightest stars of the sky — will always help us to find Corvus under all sorts of difficult conditions of light and air. Spica does not belong to Corvus ; it belongs to another constellation; yet just as one neighbor's house may help us to find another, so — in finding our way about the sky — there is much good use for neighbor-stars. The association of Corvus and Spica in our little diagram will serve, therefore, as an illustration of a method, the method of learning the stars and of finding our way about the sky by the reference of stars and groups to one another. As the "fixed" stars are not conspicuously moving about in our heavens but have retained for ages their relative po- sitions in the sky, the practice of connecting them mentally with simple lines of direction becomes full of interest and value. When, for example, your attention is once called to the fact that a short line from the two upper stars in Corvus will always go straight through Spica, the association thus suggested is not likely to be forgotten. In the same way, we have connected the Pointers in the Dipper with the Pole Star and we shall also see when we come to study Orion more closely that the row of three bright stars running diagonally through the centre will always point in one direction towards the superb white star Sinus and in the other direction toward the reddish star Aldebaran. It is also useful, at times, to have a "yard-stick" in the sky, for we may be told that a certain star is this or that number of degrees distant from another star, or that a comet on a particular night will be found 20 or 30 degrees distant from the position of the Moon. Now 15 degrees is a fairly good yard-stick; and if we can remember that the distance from Spica to the near comer of Corvus is just about 15 degrees, that the distance from end to end on the shorter side of the great quadrilateral in Orion is also about 15 degrees, and that the distance across the top of the Dipper's bowl is just 10 degrees, we shall soon be able to get a very fair idea as to proportionate distances in the sky. While in this book I shall make few references to distance in degrees, yet there are times when a general idea as to what is meant by such references is of service to us all. I will therefore refer again to this subject in now turning to the last of our key-groups. Looking South — ^June to November The star-groups at which we have been looking have been so plain in outline, and the relations they suggest have been so evident that I now prefer, in closing the series, to take something a little more difficult. I would say, however, as to the whole of this section on the key-groups, that if the beginner is not able to "make it out" at the first or second or third attempt, there need be no feeling of discouragement. The stars will be found at the times and places given them in the series of Night-Charts and Key-Maps ; their direct observation is not dependent on an understanding of the "why and how" of their move- ments. The more we can understand, the greater our pleasure is likely to be; but it is also true that the more we watch and actually observe, whether with the telescope or the unaided eyes, the more certainly shall we understand. To assume, however, — as is so often done — that we cannot find pleasure and interest in the stars till we can clearly appre- ciate the theory of their motion is as absurd as to claim that we cannot enjoy a landscape or a sunset till we can explain the how and why. As the month of June begins we shall find at 9 P. M. as we face southward that the bright star Altair and its two companions are rising on the left. As the stars rise higher and as the mists along the eastern horizon are left behind, they form a small but striking group. 28 a Beainner'0 Star*=3Booft The lowest star is not so bright as either of its companions, and yet — if the night be clear— these three almost equidistant points of light form one of the finest landmarks of the Summer sky. By 9 P.M. on June ist we shall find Altair at position A; at position B by 12:30 A.M.; at C by 4 A.M.; at D by 7 a.m., though lost in dayhght. Or, preferring to watch it marching through the months rather than through all hours of a single night, we may observe it during the early evenings of June at position A, during the early evenings of July and August as it advances from A to B ; and during the early evenings of September, October, and November from B to C and from C to D. But there are two other groups in the sky, through practically the same hours, to which I would now call your attention. Altair and its two companions point — like a straight sign-post — in two directions. As they point upward we shall find them guiding us in the general direction of Vega, the white splendid star of the constellation Lyra. It is jjtr ^ /7'-^- FOUR POSITIONS OF ALTAIR distant from Altair about twice as far as the distance between Corvus and Spica (now southwest as Altair rises) or thirty degrees. As Altair moves toward position B, Vega also will be found so much higher in the sky that, as we continue to face south, we shall have to undergo some discomfort in looking up at it. But toward this brighter star, Altair still makes, with its two companions, the same shining pointer from every position and at every hour. And this pointer directs us downward as well as upward. By the time Altair reaches position B, we shall see — by looking closely — that there is below it at a distance of a little over 20 degrees a dim group of rather small stars, — the constellation Capricomus. It is called the Sea-goat, but it looks as little like a goat as Corvus looks like a Raven. Just because its stars are not bright and its outline faint, we shall find the direction given us by Altair and its companions all the more helpful. Indeed, it is always well, whenever possible, to make the brighter groups of stars serve as guides to groups that are more obscure. For the obscure groups often possess interesting features even to the beginner. Capri- comus, for example, is one of the constellations through which the planets take their way in their march across the sky (see p. 80). It is also interesting to note that the star marked Alpha (a) may at first seem to the observer to be single ; but even an opera-glass will show that it is double, and that still another star is not far distant. Here, however, — as with the other key-groups — I have called attention to the group. learning to ©bserve 29 not for the purpose of setting forth this or that detail, but in order to illustrate the different aspects assumed by certain of the star-groups as they rise and culminate and set. A star or a group is said to culminate when it reaches its highest point in its apparent march across the sky. We have also learned how we may use our knowledge of one group to help us find another group ; and I have dwelt on all these points here at the opening of this book for the reason that each of these suggestions can be taken up and utilized as a method, the beginner going much farther than I have here gone — seeing other lines of connection and association, and thus building up, through personal interest and initiative, a star-knowledge of his own. The associations of such a knowledge will be enriched not only from our study of the skies but from the frequent references and allusions of conversation, of science, of letters. Words and phrases that were enigmas begin to have a meaning. Similes and metaphors that were quite barren become suggestive and fruitful. Much of the scientific news of the day and many of the noblest passages in the world's literature we no longer read with a sense of vague helplessness, but with at least some measure of comprehension. We know what mionth the American poet suggests as he refers to the hour "When Leo sleeps and Capricomus wakes"; and we can tell to what particular season Tennyson had reference when he wrote of the evening skies: "It fell at a time of year, When the face of night is fair on the dewy downs, And the shining daffodil dies, and the Charioteer And starry Gemini hang like glorious crowns Over Orion's grave low down in the west. That like a silent lightning under the stars She seem'd to divide in a dream from a band of the blest." Tennyson: Maud. GIACOBINI'S COMET, DECEMBER 1905. See Page Q4. lltD. Star^^flDaps for nn^ l^ear The Using of NIght-Charts and Key-Maps. Some Practical Suggestions 1 . The time-table of the maps is exactly indicated under the maps themselves. In the fuller schedule shown on p. 35 the black-letter figures indicate the hours directly covered by the map ; the other figures represent the hours for which the map thus indicated is the best approximate help. For intervening dates the map nearest in point of time will prove quite adequate. 2. The notes under the Night-Charts on the left-hand pages will be chiefly used by those who wish to employ no optical instrument. The notes under the Key-Maps on the right-hand pages will be chiefly used by possessors of opera-glass, field-glass, or telescope. 3. As the planets are constantly changing their positions they are not given on per- manent Star-Maps. On p. 82, fol., the places of the greater planets are indicated month by month for each month till the year 193 1. Jupiter, Venus, Saturn, and Mars are usually such conspicuous objects when above the horizon that the beginner may find their march through the constellations a little confusing, for they frequently obscure the outlines of the star-groups as found in the maps. Directions for their easier identification will be found, therefore, in the special section, p. 80, on the Planets. 4. The Night-Charts and Key-Maps are thus strictly confined to the stars proper. Here are shown their relations to each other and their approximate positions in the evening sky throughout the year. The lower border of each map is intended to correspond with the horizon of the observer in the latitude of New York or Chicago. Observers as far north as London will see at the horizon a little less of the southern sky ; those as far south as Richmond or Gibraltar will see at the horizon less of the sky to northward, but these differences need cause no serious confusion. 5. The upper border of each map corresponds, at the centre, with the sky overhead. The stars here are too high for convenient observation. And the stars at rising and setting are also inconveniently placed for observation, for the mists which so often obscure the horizon make difficult work both for the eyes and for the telescope. The notes placed below the Night-Charts and Key-Maps are chiefly concerned, therefore, with the star- groups that are well placed for immediate study. As all the groups repeatedly recur in the maps, the method thus indicated involves no neglect of any part of the sky. As you face due north or south begin with the sky directly before you. 6. In each case, however, the map represents somewhat more than the sky straight ahead. For each sky the map comes round a little to the right and left. In this way, the maps for north and south at any given hour cover much of the east and west also, practically presenting together the whole sky. But, as already explained (p. 4), the sky is a hollow sphere rather than a straight wall, and so there is necessarily some distortion in every map which attempts to put its figures on a fiat surface. The beginner will quickly learn to adjust himself to this difficulty if he will begin the study of each map — in its re- lation to the sky^not at the top or at the sides but at the centre. Look straight away to the north or south, and work from the centre outward. 30 Zlic ia0ln9 of tbe Cbarte 31 7. The presence of the Great Dipper, always in the sky, makes the northern groups easier to study than the southern. Moreover the southern groups, as explained on p. 25, gre absent from the sky for extended periods of time. The direction of their apparent movement, from east to west, is shown by the arrows in the upper corners of the maps. In the maps of the sky southward these arrows may be taken to suggest not only the general direction in which the constellations move but the slant or inclination of the constellation- lines, as the star-groups rise and set. This apparent slant or inclination of these figures is more clearly and fully set forth on pp. 25, 26, and 28. We see that Orion and Corvus, for example, do not march straight across the sky as though the sky were a blackboard or a picture gallery but that they follow great curves or circles through the sky's vault. This is true also of Leo: the stars of the "sickle" rise first and are also the first to set. And what is true of these groups is true of all. 8. Some of the maps will seem to the beginner to be rather full of detail; but as soon as the chief groups are learned this impression will pass away. Not that all of the fainter stars can be seen when the sky is overcast with smoke or mist. Indeed it is only on the clearest nights, when the moon is not shining, that we can get much impression of the fainter stars even to the 5th magnitude. This is especially the case in large cities where the stars are dimmed or obscured by the diffused glare of many lights. But under good conditions the smaller stars do shine forth as "the host of heaven" ; and so many of them are involved in the outlines of the constellation figures and so many are of telescopic interest that their omission would be impracticable. 9. In the study of the constellations the habit of frequently copying or drawing the outlines of the important groups will be found of great value. No matter how crude the results, and even if the observer can do no better than make a hurried sketch on the back of an envelope, the effort to record what is seen and remembered will prove a help to memory and will contribute to accuracy in observation. Naturally enough, the more carefully one draws, the greater the gain. 10. It should be said that in some of the maps a little more of the sky is included in the lower comers than can be seen at precisely the time indicated. For example, on p. 40 the constellation Canis Major, at the lower comer on the left, is not wholly risen at exactly 8 P.M. But as vSirius, its leading star, is then up, and as the whole group follows within half an hour, it seemed needless to omit the lower stars and thus sacrifice the use- fulness of the map to the literal demands of a time-table. Here, and at other points as well, I have ventured to depend upon the common sense of the student. 11. In using this book out of doors at night it is weU to be provided with one of the pocket electric flash-lights that are now available almost everywhere at very low cost. An ordinary bull's-eye lantern will do as a substitute. Better, however, than using the book out of doors at night — for any book is likely to suffer physical damage from such exposure — is the method now suggested: By using the Key-Maps in relation to the accompanying Night-Charts, familiarize yourself not only with a few clear groups but with the mental experience of relating the lines and symbols to the uncharted sky. Select your first groups not at the edges of the diagrams but as near directly north and south as practicable. Do not attempt too much at first. Then make your own drawing, on as large a scale as you like, of what you may expect to see. Take your lantern with you for the reading of your sketch, add to your sketch under the actual sky with your lantern's help, and — returning — compare the result with the maps in the book. The drawing is not essential; the method may be easily followed mentally without the drawing or the lantern; but care and precision are always worth while, especially at the first. 32 a BeQinner'0 Star^Booft 12. Telescopes are classified as to size according to the surface diameter of the lens at the large end of the instrument. A 2 -inch telescope and a "3-inch" are telescopes in which these lenses are, respectively, 2 inches and 3 inches in diameter. Further explanations of telescopic terms, and directions as to the selection and use of opera-glasses, field-glasses, and telescopes will be found on p. 97. I have usually thought it well to underestimate rather than overestimate what may be accomplished with this or that particular glass; the average eye is at first incapable of utilizing the fullest power of an instrument. There must be a little experience. The beginner with a 2-inch telescope should therefore first find and observe the easier objects suggested for the field-glass ; the beginner with a 3-inch telescope should first find and observe the objects suggested for a 2-inch; always beginning with the low-power eye-pieces. The easier objects are often the most beautiful, and it is a good principle to advance from simple tasks to greater rather than to rush to the greater, and to advance — only to disappointment 13. The numbers placed in brackets [ ] throughout the notes to the Night-Charts and Key-Maps are important. They refer to the items or paragraphs with corresponding numbers in the brief Observer's Catalogue, p. 116. There the reader will also find the pronunciation of star-names and fuller descriptions of the constellations, in alpha- betical order. Fuller accounts of the nebulae and of other objects are included. Observers possessing instruments with "hour-circles" will also find there the positions of the stars by right ascension and declination — the stellar equivalents for longitude and latitude. Information is there given as to the position angles of double and multiple stars as well as the data concerning the distances and colors of their components. Facts of this kind become of increasing interest to the amateur. They are placed in the Ob- server's Catalogue, however, partly to save space and partly because so much detail is likely, just at the first, to prove confusing to the beginner. The beginner is thus able to use the reference-numbers placed in brackets beneath the maps as much or as Httle as his interest and needs demand. 14. At the close of this book will be found maps of the two hemispheres of the sky, northern and southern. Here the constellations are all shown in their relations to each other, and the boundaries of the constellations are clearly indicated. The northern hemisphere includes a generous "overlap" of the southern sky in order that the beginner may find on a single chart most of the stars visible in Europe and the United States. The lines of right ascension and declination are here indicated: R. A. (or right ascension) representing the astronomical equivalent for longitude; S. D. (or south declination, sometimes called declination minus) representing degrees south of the celestial equator, and N. D. (or north declination) representing degrees north of it. The beginner need not go into the subject further in order to use the chart for his practical purposes in observation. If he reads in his morning newspaper, for example, that a new comet has been seen at a point in the sky described as R. A. xix hours, forty minutes; and north declination (or decHnation plus) 10 degrees, he has but to turn to his map of the northern hemisphere, and note: that as the declination is given as N. (or plus) ID degrees the object is not far from the equator, and slightly northward from it. As the equator is clearly shown (see the circle running through Orion, Serpens, Aquila, etc.) there only remains to be found the comet's position in right ascension. The R. A. of the stars is indicated by the lines running like the spokes of a wheel from the centre to the circumference of the map. These are marked at the border of the map for each "hour" in Roman numerals, from i to xxiv. As the right ascension in this case is given as xix h., 40 m., the comet is evidently in the constellation Aquila, in the general ^be "msing of tbe Cbarta 33 neighborhood of the star Gamma, — that star being not far from the point where a line marking R. A. xix h., 40m., would cross a line marking N. D. 10°. Should the reader now desire to study this region of sky in one of the earlier maps he has only to turn to "Aquila" in the Observer's Catalogue where he will find the Night-Charts and Key- Maps in which this general region is mapped for evening observation. If Aquila be not then in the evening sky and if the part of the sky in which the comet is to be seen is above the horizon only at such an hour as 2 or 3 or 4 in the morning, the observer can easily find the equivalent Key-Map by remembering that the Key-Maps with their accompanying Night-Charts are just four hours apart. This search among the maps for the approximate place of a comet may sound a little difficult in the reading, but the process is really very simple "in the doing, " and a little practice will make plain the way. 15. The English names of the Greek letters are always given in direct connection with the letters, wherever the Greek letters are used. Beginners who know no Greek — and their number, I regret to say, is growing — will soon learn these letters as they go along, without the necessity for learning the Greek alphabet all at once. For those, however, who may desire to memorize these characters quickly and as a whole, the Greek alphabet is here given in full. The vowel e, where so marked, is pronounced as a in bay ; o as o in slow; 6 as o in won; u as u in flute. a Alpha; yS Beta; ;k Gamma; (J Delta; e Epsilon; C Zgta; rj Eta; Q Theta; i I-6ta; X Kappa; A. Lambda; }i Mu; v Nu; ^Xi; o Omicron; n Pi; p Rho; a ox i Sigma; r Tau; V Upsilon ; cp Phi ; ;i: Chi ; ^ Psi ; oo Omega. The pronunciation of the names of the con- stellations, etc., is fully indicated in the Observer's Catalogue. But, as to all technical pronunciations, whether of names or letters, it should be clearly understood that these are not fundamental to one's astronomical interest. If any word be used, no matter what the language, it is well for us to use it correctly, if we may. But of more importance are the stars themselves, and no one should allow ignorance or awkwardness in using mere terms, however ancient, to destroy one's pleasure in the stars. For their clumsy nomen- clature the stars are not responsible; nor are the Greeks. Not till the i6th century of our era did the stars receive their Greek-letter designations. But an attempt at general changes would now bring confusion into the whole literature of astronomy. 16. Good photographs of star-clusters, nebulae, etc., will often prove more impressive than views of the same objects through the telescope. The beginner need not be siirprised, therefore, if his instrument fails to bring to the eye such pictures as this book contains. The camera has two advantages over any telescope, however large. First, the photo- graphic plate is more sensitive than the eye, and will always reveal more — with any particular instrument — than any eye can see. Secondly, the camera, adjusted to the telescope, may be made by a clockwork mechanism steadily to follow an object in the sky for many hours — thus permitting a very long exposure of the plate. The sensitive plate thus receives and retains, not the impression of a moment (as the eye might) but the cumulative impression of hundreds of moments. This is of incalculable advantage in recording the fainter objects of the sky. The beginner will find, however, that his own direct views, through even a small telescope, will possess, in their actuality, a charm which no photograph can ever give. The author is under many obligations for photographs to the Lick Observatory, the Mt. Wilson Solar Observatory, the Lowell Observatory, Flagstaff^ Arizona, and particularly to the Yerkes Observatory, Williams Bay, Wis. Most of these are acknowledged under the engravings. Where these acknowledgments are not explicit, credit should be given to the Yerkes Observatory, — especially for those of the moon. H (time Scbebule of tbe inigbt*®barts anb IRc^^flDaps See the Page Opposite In the table here given the maps wMch are specially drawn for the dates and hours specified are indicated by the black-letter numerals. The schedule also affords, in each case, the best approximate map for the other hours of the same evening between 6 p.m. and 12 midnight. For example, on the evening of Jan. ist, there are two sets of maps available, those for 8 p.m. on pp. 39 and 41 ; and those for 12 midnight, on pp. 43 and 45. But the latter will also do fairly well on that evening for 10 or 11 o'clock; and the former will serve fairly well for 7 or for 9. In the mid-summer raonths when the long-continued daylight obscures the stars till a late hour, the special map for the early evening (for 6 P.M. on Aug. 1st, for example) will be of little practical value in our latitudes; but the special map on that evening for 10 p.m. (for example) will meet every need. While this time schedule has particular reference only to the evening hours — showing the scope and use of the maps from, approximately, 6 p.m. to midnight — ^yet an observer who wishes to find the proper map for other hours may easily do so by remembering that the interval between the maps is just four hours. From one northward map to the next northward map is four hours. From one southward map to the next map looking southward is, similarly, four hours. The special maps for May ist, at midnight, by the time schedule, are to be foimd on pages 51 and 53. The best maps for 4 a.m. on May 2d (four hours later) would therefore be the maps that follow next in the book, — those on pp. 55 and 57. The page references throughout the time schedule are always to the Key-Maps, the Night- Chart in each case being upon the left-hand page directly opposite. These references are indicated in the time schedule for the ist and the 15th of each month; see next page. For all intervening dates the nearest map in point of time will be found adequate. The maps in which the various constellations are represented in the evening sky may be found by reference to the Observer's Catalogue. In a few instances, in which a large constella- tion is divided between north and south, reference to two successive northern or southern maps may prove desirable. 34 TIME SCHEDULE OF NIGHT-CHARTS AND KEY-MAPS The black figures show hours directly covered by maps; the other figures in same division show the hours for which the maps thus indicated are the be t approximate help. The maps for the sky as the observer faces north are in columns marked N ; those for the sky as observer faces south are in the columns marked Sv For further explanations, see opposite page. Date Hour, p.m. See Pages Date HOUE ., P.M. See Pages N S N s Jan. I 6, 7, 8, 9 39,41 Jan. I 10 , II 12 43,45 Jan. 15 7, 8, 9 39-41 Jan. 15 10 , II 12 43,45 Feb. I 6, 7, 8 39,41 Feb. I 9 10 II 43,45 Feb. 15 7, 8, 9, 10 43,45 Feb. 15 II 12 I 47,49 March I 7, 8, 9- 10 43,45 March I 10 II 12 47,49 March 15 7, 8, 9 43,45 March 15 10 II 12 47,49 April I 6, 7, 8 43,45 April I 9 10, II, 12 47,49 April 15 7, 8, 9> 10 47,49 April 15 II 12 I 51,53 May- I 7, 8, 9, 10 47,49 May I 10 II 13 51,53 May 15 7, 8, 9 47,49 May 15 10 II) 12 51,53 June I 6, 7. 8 47,49 June I 9 10, II, 12 51,53 June 15 8, 9, 10 II 51,53 June 15 II 12, I 55,57 July I 7, 8, 9- 10 51, 53 July I 10 II, 12 55,57 July 15 7, 8, 9 51,53 July 15 10 "j 12 55,57 Aug. I 6, 7, 8 51,53 Aug. I 9 10, II, 12 55,57 Aug. 15 8, 9, 10, II 55,57 Aug. 15 II 12, I 59,61 Sept. I 7. 8, 9. 10 55,- 57 Sept. I 10, II, 12 59,61 Sept. 15 7, 8, 9 55, 57 Sept. 15 10 II, 12 59,61 Oct. I 6, 7, 8 55, 57 Oct. I 9 10, II, 12 59,61 Oct. 15 7, 8, 9, 10 59, 61 Oct. 15 II 12, I 39,41 Nov. *i 1, 8, 9, 10 59, 61 Nov. I 10 II 12 39,41 Nov. 15 7, 8, 9 59, 61 Nov. 15 10 II, 12 39,41 Dec. I 6, 7, 8 59, 61 Dec. I 9 10, II, 12 39,41 Dec. 15 7, 8, 9> 10 39,41 Dec. 15 II 12 I 43,45 Dec. 25 6:> 30,8 :30,9:30 39,41 Dec. 25 10 :30, 12:30 43,45 35 SPIRAL NEBULA IN TRIANGULUM, KNOWN AS MESSIER 33 From a photograph taken at the Yerkes Observatory 36 for Un^ IPear 37 a Beainnefs Stai^Book NIGHT-CHART TO THE SKY AS THE OBSERVER FACES NORTH. JAN. 1, 8 P.M., DEC. 15, 9 P.M., DEC. 1, 10 P.M., NOV. 15, 11 P.M., NOV. 1, 12 P.M. FOR KEY-MAP TO THIS CHART SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES SOUTH, SEE PP. 4O, 4I. For the sky at other Dates and Hours see Time Schedule, p. 35. The Constellations. For the Telescopic Objects See the Page Opposite. Numbers in brackets [ ] refer to correspoftding numbered notes in Observer's Catalogue, p. Il6. As we face the north we now find the Great Dipper low down in the slcy, wheeling slightly upward toward the right. Its apparent motion round the pole is described on p. 23. Having found the Pole-star, let us note the group called "the Little Dipper," for the Pole-star is at the tip of its handle. Some of its stars are quite faint, and except with an opera-glass are not easy to see, save on very clear nights. The Little Dipper forms part of the constellation called Ursa Minor [405] or the Little Bear, just as the Great Dipper forms part of a larger constellation called Ursa Major [400] or the Great Bear. In each case the stars convey no clear impression of a bear, and such outlines of mythological or animal figures are so unimportant that inability to trace them need cause no discouragement. The handle of the Dipper is the tail of the bear; the bowl is the animal's hip; the ears are at the little group marked Rho (p) and Sigma (o-) ; the nose is at Omicron (0) ; the forefeet are at Iota (i) and Kappa (k); the hind feet at Lambda (X) and at Xi (|). Let us again follow with our eyes the line from the Pointers (a and P) in the Great Dipper to the Pole-star; and let us imagine that we are continuing this line in the same direction right on across the northern sky. Just above this continued line, quite high up, you will see the W-shaped figure which represents the chair of Cassiopeia [80]. Just below, you will see the fainter stars of Cepheus [100] making a sort of house-shaped figure with roof now pointing to the east. Below the group just mentioned we may see the head of Draco, the Dragon [160], formed by the stars Gamma (7), Beta (P), Nu (v), and Xi (|). To the west of Draco, or toward the left, we may note Cygnus, the Swan [145]. The stars Deneb [146] etc., form, as you will see, the figure of the Northern Cross, or, if we wish to find in the same stars the figure of the flying swan, the head will be at Beta (P), the tail at Alpha (a), and the tips of the wings at Delta (8) and Epsilon (e). To the left of Cygnus and quite to the west you will see Delphinus, the Dolphin [155], with its pretty diamond-shaped figure; and, below, you will note Sagitta, the Arrow [335]. Below Cygnus and the Cross and to the right you will find the small but important constellation, Lyra, or the Lyre [260]. These stars will soon be setting. The star Vega [261], bluish white, is one of the brightest in the sky. Lyra can always be identified by the four-sided figure of the small stars Delta (8), Gamma (7), Beta (P), and Zeta (J). Toward a point in space quite near to Vega our Sun, see p. 66, is moving at the rate of more than 720 miles a minute, taking with him the earth and all the planets of our solar system. So vast, however, are the distances of space that only an infinites- imal fraction of the journey is traversed in a century of time. As Vega sets, you will see far toward your right, at the north-east and very low down, the first stars of Leo, the Lion [225], rising. You may have to wait a few rninutes ere you can make them out. Of these stars, forming — as you see — a figure like a sickle, the brightest is Regulus [226]. Above Regulus are the faint stars of Cancer [50], the Crab; and the brighter stars of Gemini [185], the Twins, shown more fully in our next map. Of Leo we will speak again when the whole constellation is higher up and in better position for observation; see p. 44. The stars here shown lead the way, however, and the figure of the sickle serves as a convenient sign of identification. The stars of Cancer are not bright, and on dull nights they are not easy to find except with an opera- glass or field-glass. But on a very clear evening the pretty star cluster called Praesepe or the Bee-hive [52], can be recognized like a tiny patch of cloud, even with the unaided eye. A telescope of low power will show the twinkling of its many suns. Jfor ®pera»«(5Ias0, jfielb^Clase, ant) telescope 39 KEY-MAP TO THE SKY AS THE OBSERVER FACES NORTH. JAN. 1, 8 P.M., DEC. IS, 9 P.M., DEC. 1, 10 P.M., NOV. 15, 11 P.M., NOV. 1, 12 P.M. FOR NIGHT-CHART TO THIS MAP SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES SOUTH, SEE PP. 40, 4I. For the sky at other Dates and Hours see Time Schedule, p. 35. The Telescopic Objects. For the Constellations See the Page Opposite. Numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. ii6. I. For OPERA-GLASS AND FIELD-GLASS there are fine star-fields through Cassiopeia [8o] and Cygnus [145]. Here lie some of the richest sections of the Galaxy or Milky Way (see p. 19). We can see that it is made up of innumerable stars closely massed together. In Lyra [260] the star marked Epsilon (c) can, with opera-glass or field-glass, be seen as double. In a tele- scope 334 in. or over, it will be found a quadruple, or double-double [263]. In Cygnus almost on a line between Alpha (o) and Delta (S) there are two neighbor stars marked Omicron (o) [148] making — with the star 32 [149] — the centre of a pretty field. Near the foot of the cross the little star marked 6 — though in another con- stellation — is an easy double for a field-glass [426]. A field-glass, steadily held, will also divide the stars marked Delta (8) and Zeta (?) [266, 265] in Lyra, and Nu (v) in the head of Draco [i 62]. Note with the opera-glass the little star marked g near Mizar [401] in the Great Dip- per. Itsnameis Alcor[402]. Mizar and Alcor together were called by the Arabs "the horse and his rider." II. With a two-inch telescope the star-fields of Cygnus and Cassiopeia are even more interesting than with a field-glass. For these and all the other objects thus far noted use a low-power eyepiece. In addition to the above try Beta (P) [262] in Lyra, and also Beta (P) in Cygnus at the foot of the Cross, one of the finest objects within the range of a small instrument [147]. The colors of the components are orange and blue. Farther to the west a pretty double is also found in the Gamma (7) of Delphinus [157]. Turning again to the north, we shall find more inter- esting still the star Mizar [401] to which we have already referred, in the bend of the Dipper's handle. In addition to the little star Alcor a two-inch telescope will show that Mizar is itself a double star, one com- ponent a brilliant white, the other a pale emerald. Another, fainter, star is also visible, so that with Alcor four objects appear in the field of the telescope. In Cepheus note the easy doubles, Delta (8) [loi], Xi (i) [103], and Beta (P) [102]. The last is the most difficult. Toward the right and at the northeast, double stars for a two-inch glass will also be found in Cancer [50]. Try the stars Iota (i) and Zeta (l) [53- 54]- A charming star-cluster will be found here in Praesepe [52] or the Bee-hive. It may be readily found by drawing an imaginary line from Castor to Pollux and continuing it downward. The sparkling "star-dust" of the cluster will be found slightly to the left of it. III. With a three-inch telescope all the pre- ceding objects are, of course, even more available. In addition to the preceding, the observer can now try to divide Polaris, the Pole-star (406], by using a magni- fying power of 75 to 100. The companion is not very close; it is difficult to see only because of the dis- proportionate brightness of the larger component. Other stars for a three-inch telescope are Mu (n) [153] near Lacerta, and 61 [150] as well as 17 [152] and Chi (x) [151] in Cygnus; Omicron (o) [163] in Draco; Alpha (a) [261] and Eta (r]) [264] in Lyra, though the former is difficult for the beginner ; indeed a 3H or 4-inch telescope may be necessary. To the extreme right, try the Gamma (7) [227] of Leo — a much more satisfactory object. This star is a binary, the two components being in slow revolution about a common centre of gravity. Of the stars of Gemini we will speak on p. 41 ; and the objects in constellations above the Pole we will discuss when they are in better position for observation. Of the clusters, that in Cancer named Praesepe [52], and that marked M 39 [154] (found by an imaginary line from Beta (P) to Gamma (7) in Cygnus, projected onward) make fine objects if viewed with a low-power eyepiece. There are also beautiful star-fields near the star Gamma (7) in Cygnus and near the garnet star Mu (n) [104] in the constellation Cepheus. a Beglnner'0 Star^Book NIGHT-CHART TO THE SKY AS THE OBSERVER FACES SOUTH. JAN. 1, a P.M., DEC. 15, 9 P.M., DEC. 1, 10 P.M., NOV. 15, 11 P.M., NOV. 1, 12 P.M. FOR KEY-MAP TO THIS CHART SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES NORTH, SEE PP. 38, 39. For the sky at other Dates and Hours see Time Schedule, p. 35. The Constellations. For the Telescopic Objects See the Page Opposite. Numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. ii6. As we face directly south, the east is of course upon our left hand. The stars that are now moving round from east to south present a superb spectacle. In Orion [290] note first the two stars of the first magnitude, Betelgeuze [291] and Rigel [292]. The former marks the right shoulder of the giant huntsman: the latter his left knee. His head is at Lambda (X) and the tip of his uplifted club at Nu (v). The three bright stars Zeta (S), Epsilon (e), and Delta (8) mark his belt, from which his sword hangs down- ward with its tip at Theta (fl). To the left of Orion Hes the dim group Monoceros [270] or the Unicorn, so unimportant that the beginner may well omit it till other groups are learned. Higher up are the stars of Gemini, the Twins [185]. The heads are marked by Castor [186] and Pollux [187], named from the devoted comrades of the ancient myth. The three bright stars of Orion's belt, running diago- nally through the oblong figure which marks his body, will point us upward toward the red star Aldebaran [381] and, still farther on, to the Pleiades [382], the most beautiful of the star-clusters. Near Aldebaran is another cluster called the Hyades [383], not so thickly massed but almost as interesting. Both these clusters are in the constellation Taurus, the Bull [380]. Aldebaran is the Bull's red eye, the nose is at Gamma (7), the horns stretch away to Zeta (?) and Beta (P). The imaginary figure of the Bull, as with that of Orion, is incomplete. Again taking our direction from the line of Orion's belt we find it pointing us in the other direction to SiRlus [66], the brightest of all the stars, — supposed to mark the eye in the constellation, Canis Major, the Great Dog [65]. The dog sits upright with forepaws at Beta (P), ears at Gamma (7) and his hind feet at Zeta (t). To the right of these stars and a little lower down is CoLUMBA, the Dove [125]; and a line from this group drawn through Sirius and carried onward will bring us to Canis Minor, the Little Dog [70]. Its stars form no outline of a dog; but among them is Pr6cyon [71], a fine first-magnitude star. To the right of Sirius and just below Orion are the stars of Lepus, the Hare [240], and to the right of Lepus stretches the long line of Eridanus [175], the River, taking its rise near Rigel. Returning now to Taurus, we find that the triangular figure which has its apex at Gamma (7) points us downward to the huge constellation of Cetus, the Whale [no]. For Mir A, see p. 14. Above Cetus stretch the dim stars of Pisces, the Fishes [320], starting from the point at Alpha (a) and forming to the westward a pretty chaplet of small stars at Theta (9), Lambda (X), Gamma (7), etc. Except on very clear nights some of these are not easily found without an opera-glass. To the right of the Pleiades lie the three bright stars that mark the small constellation of Aries, the Ram [30]; and above Aries shines the three-cornered figure of Triangulum, the Triangle [395]. Both groups are now too high for convenient study; but see p. 55. In now looking to the right to the great square of Pegasus, the Winged Horse [301], it will help us to assume that the upper corner of the map comes in toward us a little and that all the lines slant somewhat downward as indicated by the arrow in the corner; see p. 4. Far to the south-west, Aquarius, the Water -Bearer [15], is setting, the mouth of the water-jar being marked by the little Y-shaped figure at Gamma (7). Still further to the southward lies Piscis AusTRiNus, the Southern Fish [330], not to be confused with Pisces, the Fishes, to which we have just referred. The mouth of the Southern Fish is marked by FomalhauT [331], a star of the first magnitude. It is not so bright as Sirius or Rigel but a welcome object in this vast region of less brilliant sky. It sets, in the latitude of New York, just as Sirius rises. In the latitude of London it sets a little earlier. Jfor ®pera=»(5Ia00, Jfielb*(51as0, anb telescope 41 OC/usfeFf Of f\Jebuia. a COLi/MB/l /*3 f/}e otfserfer faces Soufhu/ard, the Jtars af his left are risina; those ath's right aru sefftnif. KEY-MAP TO THE SKY AS THE OBSERVER FACES SOUTH. JAN. 1, 8 P.M.. DEC. 15, 9 P.M., DEC. 1, 10 P.M., NOV. 15, 11 P.M., NOV. 1, 12 P.M. FOR NIGHT-CHART TO THIS MAP SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES NORTH, SEE PP. 38, 39. For the sky at other Dates and Hours see Time Schedule, p. 35. The Telescopic Objects. For the Constellations See the Page Opposite. Numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. Ii6. I. With opera-glass or field-glass examine the two star-clusters in Taurus, the Pleiades [382] and the Hyades [383]. The glass will greatly increase the charm and the interest of both groups; see p. 18. Near Aldebaran note the pretty doubles Theta (9) and Sigma ( FOR THE SKY AS THE OBSERVER FACES SOUTH, SEE PP. 48, 49. -, -, r "5 For the sky at other Dates and Hours see Time Schedule, p. 35. ' b ' " The Telescopic Objects. For the Constellations See the Page Opposite. Numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. Ii6. I. For OPERA-GLASS AND FIELD-GLASS there are rich fields through the Milky Way, here stretching low down from north to west. Note especially the regions near Epsilon («) in Auriga, near Alpha (a) in Perseus, and near Gamma (7) in Cassiopeia. Further still to west- ward there are charming views in the Hyades [383] near the red star Aldeb'aran, and in the Pleiades [382]. The names of the brighter stars in the Pleiades are given in the Observer's Catalogue. See also pp. 18, 19. They are now setting, but with the evenings of Autumn we shall find them again at the northeast. Turning, now, to the eastward or to the right, we find some easy double stars. Among these are the Delta (S) [loi] of Cepheus; Nu (v) [162] in the head of Draco; and Delta (8) [266], Zeta (5) [265], and Epsilon (e) [263] in Lyra. These can all be divided by a field-glass, steadily held. The last named star is the famous ' ' double- double, ' ' — for a telescope of three and one-quarter or three and one-half inches will show that each of its two components is itself a double. Above Lyra, note the star-cluster in Hercules marked M 13 [206]. An opera- glass will barely show its existence and a field-glass will show it only as a very small globular patch of mist. A telescope of two or three or four inches will show in increasing measure the real nature of the object; but a large instrument, six to eight inches in aperture, is neces- sary to illustrate the basis of Herschel's opinion that it contains at least 14,000 stars. An object as beautiful, and more within range of a good field-glass, is the double cluster, x-h [309], in Perseus. Above Hercules let us note with the opera-glass the beautiful circlet of stars which form Corona [130]. II., With a two-inch telescope, using an eye-piece of low power, the preceding objects are even more inter- esting than in the field-glass. The finest double star for a two-inch instrument is Zeta (t) [401] in the bend of the Great Dipper's handle, but it is now inconveniently high. So also are the pretty doubles iz and 15 [61, 62] in Canes Venatici. Well placed for observation, however, are such fine objects as the Beta (P) [102] and Xi ({) [103] in Cepheus; the Beta (P) in Lyra [262]; and the Delta (8) [202] and Alpha (a) [201] in Hercules. The last will require an eye-piece of higher power, but it is an object of singular charm. Note also the Tau W [387], Phi (4>), [391], and Eta (i\), [384] of Taurus; and the Gamma (7) [3] of Andromeda — though this beauti- ful object is almost too low; and try the star in Auriga marked 14 [38]. Also examine the cluster M 34 [311] in Perseus. III. With a three-inch telescope, first observe the objects already specified for the field-glass and the two-inch. These are appropriate for any instrument, however large. Then attempt Polaris, or the Pole- Star [406]. The small blue companion is now — as viewed in an astronomical telescope — almost directly above the brighter component. With an eye-piece hav- ing a power of from 75 to 100, the night being clear, there will be little difficulty in seeing it. Vega [261], the beau- tiful first-magnitude star of Lyra, is an even more difficult double than the Pole-Star, for a telescope of three and one-quarter or three and one-half inches is usually neces- sary for its division. Other and easier doubles for a three-inch are the stars marked Rho (p) [204], Mu (h.) [203], and gs [205] in Hercules; Zeta (£) [131] in Corona; and Iota (i) [164], Omicron (o), [163], and Gamma (7) [165] in Draco. The last may be too difficult. Try it, however, as well as the Eta (i)) [264] in Lyra; the Eta (1]) [308] and Zeta (t) [310] in Perseus; and the fine binary star Eta (11) [82] in Cassiopeia. In addition to the clusters specified for the two-inch, there is the cluster between Hercules and Draco marked M 92 [207]. It is almost on a line between the stars Pi (ir) in Hercules and Beta (P) in Draco. While not of such intrinsic interest as M 13 [206], it is almost as satisfactory an object in a three-inch instrument. a Befilnner'0 Star^Booft NIGHT-CHART TO THE SKY AS THE OBSERVER FACES SOUTH. MAY 1, S P.M., APRIL 15, 9 P.M., APRIL 1, 10 P.M., MARCH 15, 11 P.M., MARCH 1, 12 P.M. FOR KEY-MAP TO THIS CHART SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES NORTH, SEE PP. 46, 47. For the sky at other Dates and Hours^ee Time Schedule, p. 35. The Constellations. For the Telescopic Objects See -the Page Opposite. Numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. ii6. As we now face southward, we find the constellation Leo, the Lion [225], directly before us. Leo is rather high at present, but the group is easily recognized from the figure of "the sickle," formed by the stars Alpha (a) or Regulus, and Eta (tj). Gamma (7), Zeta (J), Mu (n), and Epsilon (c). Regulus [226] is a first magnitude star, but as it lies in the track of the planets, see p. 80, it is sometimes outshone by the brightness of Jupiter, Mars, or Venus. Below Leo lies the small constella- tion Sextans, the Sextant [375], faint and unimportant; and, lower still, the stars of Hydra, the Water-Snake [210], stretch their long course almost to the eastern horizon. The faint stars of Crater, the Cup [140], were at one time regarded as part of Hydra, but they are now mapped separately. Corvus, the Crow — or the Raven, — is more clearly seen and is more important [135]. From the diagram on p. 26 we have learned to associate Cor- vus with the bright star Spica [416], and to note how the line from Gamma (7) to Delta (8) points to Spica from every position and at every hour. Of all the first- magnitude stars Spica is one of the whitest in color. Virgo [415], to which this star belongs, has represented a Virgin or Maid for untold centuries, among Chaldees, Egyptians, Greeks — and even among the Chinese. The figure is not clearly marked, the head being near Nu (v), the waist at Gamma (7), the feet at Kappa (k) and Mu (|i), the right hand at Epsilon (e), and the left arm ex- tended at the side, bearing a sheaf of wheat with its head at Spica. To the left of Virgo, and just rising, are the stars of Libra [245], the Balances or Scales. Above Virgo and to the left of Leo are the masses of little stars — extremely pretty in an opera-glass — called Coma Berenices or Berenice's Hair [120]. To the west of Leo lie the faint stars of Cancer I50]. Next is the constellation Gemini, the Twins [185], its lines pointing more directly downward than can be here indicated in the map. Castor [186] and Pollux [187] make one of the finest pairs in the sky, and not far away to the southwest is another pair, the first-magnitude star Pro'cyon and the neighboring Beta 0) in the small constellation called Canis Minor, the Little Dog [70]. There is no danger of confusion, however, for in the latter pair the difference in brightness is marked. As Orion [290] sets, the uprightness of the figure here should be corrected by the figure of the group at position C on p. 25. Canis Major, the Great Dog [65], is also setting, as is Lepus, the Hare [240], but all that we can discern of the former in latitudes as far north as New York, is the departing flash of the great SiRlus [66]. Still facing south, but again turning eastward — to the left, — we may note the constellation Bootes, the Herds- man [40], distinguished for us by Arcturus [41], one of the noblest of the first-magnitude stars. The constel- lation forms a kite-like figure, and we have already indicated the mythical outline of the Herdsman, p. 42. It contains nothing else so interesting, however, as its brightest star, of which — under its reference number — we have spoken in the Observer's Catalogue. At the high velocity there indicated, Arcturus is rushing through space — according to Newcomb — toward the southwest, or in the general direction of the constellation Virgo. Before leaving this map, let us note what has sometimes been called "the Diamond of Virgo." It is formed by four stars. These are Spica, Arcturus, the Beta (p) of Leo — called Deneb'ola, — and the star in Canes Venatici, the Hunting Dogs, which bears the mark 12. It is often called "Cor Caroli," the Heart of Charles [61], after Charles II. of England. The little constellation to which the last star belongs has never contained an outUne of a Hunting Dog or of anything else, but the diamond-shaped figure pust noted is strikingly beautiful and, when once recognized, is not easily forgotten. It may also be noted that a straight line across the sky is formed by the three bright stars Spica, Regulus, and Pollux — almost equidistant. Jfor ®pera*(5la50, jTielb^^BIaas, an& telescope 49 ^Ist^ZHdrndrd'^m'^thond under 0C/u5ter ort^eouya C£NTAUf?US • » ' oaser-i'or^acfjSoufhu'ar-d, // Ihc slarjdf hts Ir^rfare rijtnij ; CJii °c thost? at h/5 r-itfhf ore Jeffing. KEY-MAP TO THE SKY AS THE OBSERVER FACES SOUTH. MAY 1, 8 P.M., APRIL 15, 9 P.M., APRIL 1, 10 P.M., MARCH 15, 11 P.M., MARCH 1, 12 P.M. FOR NIGHT-CHART TO THIS MAP SEE OPPOSITE PAGE, FOR THE SKV AS THE OBSERVER FACES NORTH, SEE PP. 46, 47. For the sky at other Dates and Hours see Time Schedule, p. 35. The Telescopic Objects. For the Constellations See the Page Opposite. Numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. Ii6. I. With opera-glass or field-glass examine, first, the region to the left, or east, of Leo covered by the constellation Coma Berenices, — "Berenice's Hair." The mythical story connected with these little stars is told in the Observer's Catalogue [120]. The scene on a clear night, when there is no moonlight to outshine their twinkling, is full of charm. The regions of Orion and Canis Major, at the extreme ■west, will repay us quite as well so long as these groups are in the sky. Here see column i, pp. 40 and 41; but all the stars near this right-hand border are too near the horizon for satisfactory observation. The lines of Gemini run much more directly downward than our map can indicate; as to Orion see p. 25. If we run a line, however, from Castor to Pollux and continue it on- ward we shall find just to the left of this line the pretty cluster, in Cancer, called Praesepe, or the Bee-hive [52]. We may also find it by searching just before the "sickle" of Leo. It is practically on a line, from Beta (P) in Leo to Eta (rj), projected onward an almost equal distance. Among the wide double stars that may be divided by a field-glass, steadily held, are Gamma iS) (242] in Lepus, just below Orion; Tau (t) in Leo [228]; and Alpha (a) [246] in Libra. II. With a two-inch telescope, note first such star clusters as that marked M 41 [67] in Canis Major; that in Gemini marked M 35 [188]; those marked merely with Uttle circles in Monoceros near the stars 30 [275], and Delta (8) [273], and Epsilon (e) [274]; that marked M 53 [121] in Coma Berenices. The easiest for a small instrument is, of course, Praesepe [52] in Cancer. Among the double stars for a two-inch telescope, three superb objects are now available: Castor [186] in Gemini; the star Gamma (7) [417] in Virgo; and Gam- ma (7) [227] in the "sickle" of Leo. The last is the most difficult. There is a little "neighbor star," only connected optically with the pair, that should not be confused with the real companion of the primary star. The two components of the binary system are very close together in the field of a two-inch, and a good glass with a steady mounting is requisite for their division. Castor is also a superb object. Use for each of these stars a power of from 65 to 75. Gamma (7) in Virgo is an, easier object, not requiring powers quite so high and therefore a more beautiful pair for the beginner. Other double or multiple stars for the two-inch are Pi (it) [44] and Delta (8) [43] in Bootes; Alpha (a) [246] in Libra; Delta (8) [136] in CoRVUs; Tau (t) [228] in Leo; Iota (i) [53] and Zeta (S) [54] in Cancer; Delta (8) [190] and Zeta (?) [193] in Gemini; Beta (P) [271] and Epsilon (e) [272] in Monoceros, and 14 [72] in Canis Minor. The double stars further to the westward are noted on p. 45. They are here too near the horizon for satisfactory observation. III. With a three-inch telescope, first examine the preceding objects. Each is not only appropriate for a three-inch but it may be viewed in such an instru- ment under far better conditions. With eye-pieces of the same power the field of view will be larger and it will be illuminated more clearly and brightly. It is also easier, first using an eye-piece of low power, to find the objects specified. To the star-clusters just mentioned add M 46 [26], almost on a line projected from SiRius through the Gamma (7) of Canis Major; and M 67 [SSli between Cancer and the head of Hydra. With eye-piece of lowest power sweep through the region of Virgo just west of Epsilon (e). This is a region of many nebulae too faint in our small instruments for individual classification. Add to the double-stars Alpha (a) [416], Theta (9) [418], and Tau (t) [419] in Virgo; Epsilon (e) [191], Kappa (k) [189], Nu (v) [194], and Lambda (X) [192] in Gemini. The last is the unmarked star form- ing a small triangle with Delta (8) and Zeta (J). Try, also, Epsilon («) [212] in Hydra, and Beta (P) [229] in Leo. The track of the planets lies here through Gemini, Cancer, Leo, Virgo, and Libra; see p. 80. 50 a ^Beginner's Star^Book NIGHT-CHART TO THE SKY AS THE OBSERVER FACES NORTH. JULY 1, e P.M., JUNE IS, 9 P.M., JUNE 1, 10 P.M., MAY 15, 11 P.M., MAY 1, 12 P.M. FOR KEY-MAP TO THIS CHART SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES SOUTH, SEE PP. 52, 53. For the sky at other Dates and Hours see Time Schedule, p. 35. The Constellations. For the Telescopic Objects See the Page Opposite. The numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. Ii6. Looking northward, we now find the Great Dipper, part of the constellation Ursa Major [400], high up but slowly wheeling downward. The bowl precedes the handle; and as shown on p. 23, it has now passed through position C and is moving toward position D. The handle of the Dipper was supposed to represent the Bear's tail; the hip being at the Dipper's bowl, the hind feet at Mu (|i.) and at Xi (?), the forefeet at Kappa (k), the ears at the little stars Sigma (o-), etc., and the nose at Omicron (o). The Bear now has his head downward, his back being toward the Pole. The stars really form no like- ness to this animal or to any other. The line of direction to Polaris, the Pole-Star, may be taken at every hour from the stars Alpha (a) and Beta (P) in the Great Dipper, and this line now points down- ward and toward the right. Polaris [406] is at the tip of the handle of the Little Dipper, part of the constel- lation Ursa Minor, or the Little Bear [405]. If we continue this line straight on across the sky, it will pass between the house-shaped figure of Cepheus [100], and the brighter group called Cassiopeia [80], or The Lady of the Chair. The line will cut through Cepheus not far from the star Gamma (7), and, passing on, will "find " the star Beta (P) in Pegasus [301] when it rises above the horizon; see p. 54. The line will traverse an unim- portant group called Lacerta, the Lizard [220]. The stars below this line are not high enough to be well seen, though the figure of the W, which represents the Chair of Cassiopeia, will doubtless be clearly marked. Above this line, however, lie three most interesting constella- tions. First among these, let us note Cygnus, the Swan [145]. The head is supposed to be at Beta (P), the tips of the outstretched wings at Delta (8) and Epsilon (e), and the tail at Alpha (o) or Deneb [146]. These stars are more frequently regarded, however, as the Northern Cross; and when the figure is once recognized it is not easily forgotten. Eastward from Cygnus, or further to the right, shines the small constellation called Delphinus, the Dolphin [155]. It presents no outline of a dolphin but four of its stars do form a very pretty diamond. Turning rnore directly northward, and looking higher, we may see — above Cygnus — the figure of Lyra, the Lyre [260J, with its fine first-magnitude star Vega [261]. Further to our left from Vega we can detect the head of Draco, the Dragon [160], with the winding stars of this constellation looped, as it were, in a figure like an arch, above the bowl of the Little Dipper. The head of Draco can always be found, when Cygnus is in the sky, by the arms of the cross, — for a line drawn through them, from Epsilon (e) to Delta (8), will always point toward Gamma (7), Draco's brightest star. A line from this star to Beta (P) at the foot of the cross will point directly to the little constellation Sagitta, the Arrow [335], lying, as does Cygnus, full in the Milky Way. Below the Pole, too far down for good observation, lie the fine constellations Perseus [305], and Auriga, the Charioteer [35]. Capella [36], the beautiful first- magnitude star of the latter group, is so brilliant that it may often be seen through the mists of the horizon until almost the very moment of its setting. With Beta (P) of the same constellation, it forms a pair often mistaken for Castor and Pollux, the companion stars of Gemini, the Twins [185]. These are now further to the westward. It should be noted, however, that the latter stars are nearer together — with the brighter above; not below, as in the case of the two bright stars of Auriga. The dim stars of Cancer [50] can hardly be seen so near the horizon, but above them shines the "sickle" of Leo [225]. This is not turned down quite so far as shown here, nor is it turned up quite so far as shown in the next map, p. 53, but the sickle does lead the way downward, the other lines of the figure stretching back- ward and upward from it. Lynx [255], and Leo Minor [235], the Little Lion, are not important. fov ®pera*(5Ia00, jTielb^'CBIass, anb telescope 51 KEY-MAP TO THE SKY AS THE OBSERVER FACES NORTH. JUUY 1, 8 P.M., JUNE IS, 9 P.M., JUNE 1, 10 P.M., MAY IS, 11 P.M., MAY 1, 12 P.M. FOR NIGHT-CHART TO THIS MAP SEE OPPOSITE PAGE. , I i FOR THE SKY AS THE OBSERVER FACES SOUTH, SEE PP. 52, 53. ^ For the sky at other Dates and Hours see Time Schedule, p. 35. The Telescopic Objects. For the Constellations See the Page Opposite. The numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. ii6. I. With opera-glass or field-glass follow, first, the course of the Milky Way as it stretches through Auriga, Perseus, Cassiopeia, and on through Cepheus, Cygnus, and Sagitta. The innumerable stars which compose it are massed more thickly at some points than at others. Near Alpha (a) in Perseus, Gamma (7) in Cassiopeia, and along the line of the Cross in Cygnus — particularly from Gamma (7) to Beta (P) — there are regions of especial beauty and charm. Note also the fine double cluster in Perseus, lying almost on a line between Eta (r)) in that constellation and Epsilon (e) in Cassiopeia. It is marked x-h [309]. Just now, however, it is too low — except in far northern latitudes — for satisfactory observation. Among the wide double stars, the following may be divided by a field-glass, if the glass be steadily held: the Nu (v) [162] in the head of Draco; Epsilon (e) [263], Delta (8) [266], and Zeta {t) [265] in Lyra; Delta (8) [loi] in Cepheus; and Omicron (o) [148] in Cygnus. Near the foot of the Cross note also the little star marked 6 [426]. MiZAR is the name of the star marked Zeta (t) [401] at the bend of the Dipper's handle. Quite near, and involved in the same stellar system with the brighter star, is the small star marked g. Its name is Alcor [402]. As will be seen under the reference number in the Observer's Catalogue [401], recently discovered facts have given new interest to these well-known stars. II. With a two-inch telescope the beginner should first examine the preceding objects. Mizar, however, to which we have just referred, is rather high just now for convenient study. Toward the west — if the mists of the horizon have not clouded them — be sure to examine Castor [186] in Gemini and Gamma (7) [227] in Leo. Both are fine objects; the latter the more difficult of the two. The beginner need not feel discouraged if his first attempt to separate the components should not succeed. Near to Gamma (7) is also a small "neighbor star" having only an optical connection with the binary system; see p. 13. The real double is a very close pair in either a two-inch or three-inch instrument. But whatever the disappointments in connection with the preceding star there will be none with the Beta (P) [147] of Cygnus, extremely easy and yet singularly fine. A little closer and yet also a delightfully satisfactory object is the Gamma (7) [157] of Delphinus. Easy objects will also be found in the Xi (|) [103] and Beta (P) [102] of Cepheus; in the Beta (P) [262] of Lyra; in the Zeta (l) [54] and Iota (t) [53] of Cancer; in the IQ of Lynx [256]; and in the Delta (8) [190] and Zeta (J) [193] of Gemini — if the last named stars be not too near their setting to be clearly seen. III. With a three-inch telescope the objects already specified may be seen to even better advantage than with the two-inch. All should be viewed with an eye-piece of low power (from 40 x to 60 x) except in the cases of the Gamma (7) [227] in Leo and Castor [186] in Gemini. In the latter case 60 x will sometimes prove sufficient, though 75 x is better. Powers between 60 and no will also be needed for some of the following: the Eta (t]) [82] in Cassiopeia, one of the finest of binary systems; the Mu ((«.) [153] of Cygnus, just to the right, or east, of Lacerta; and 61 [150], Omicron (o) [148], and // [152], also in Cygnus; as well as Eta (tj) [308] in Perseus; and Omicron (o) [163], Iota (i) [164], and Gamma (7) [165] in Draco. In Gemini, if the stars are not too low in the sky, try Kappa (k) [189], Epsilon [191], and Lambda (X) [192]. The last is the unmarked star which forms a small triangle with Delta (8) and Zeta (J), both of which we have already mentioned. On a line extending the handle of the Little Dipper note the small star marked JQ H [49]. Ir trying to divide Polaris, the Pole-Star [406], use an eye-piece affording a power of from 75 to 100 on a three-inch instrument. At the present hour, the begin- ner may look for the small blue companion upward and toward the left from the brighter component. 52 a Beginner's Star«»Booft NIGHT-CHART TO THE SKY AS THE OBSERVER FACES SOUTH. JULY 1, a P.M., JUNE 15, 9 P.M., JUNE 1, 10 P.M., MAY 15, 11 P.M., MAY 1, 12 P.M. FOR KEY-MAP TO THIS CHART SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES NORTH, SEE PP. 50, 5I. For the sky at other Dates and Hours see Time Schedule, p. 35. The Constellations. For the Telescopic Objects See the Page Opposite. The numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. ii6. As we face toward the south, the stars of Scorpio, or ScoRPius [350], lie before us — a little to the left. Scorpio rises at about the time Orion sets, and dominates the sky of midsummer almost as strikingly as Orion [290] dominates the sky of winter. We may recognize the constellation, even through the haze which so often lies near the horizon, by the fan-like figure of six bright stars. This is formed of two groups, of three each. Alpha (o) or Antares [351] with Tau (t) and Sigma (o-) form one group, pointing directly to the other— Beta (P), Delta (8), and Pi (ir). These stars— always in the same fixed relation to each other — may often be seen when the rest of Scorpio is practically blotted out by fog or mist. The whole figure is so like the scorpion of the tropics, with its extended ' claws at Gamma (7) and Xi (?), — its tail at Epsilon («) and Mu ((*) — extending to its sting at Lambda (X), that it is the most realistic of the constellation outlines. Directly to the west, or to the right, of Scorpio shine the stars of Libra [245] — the Balances or Scales. The fainter stars are not always visible, except when the night is very clear, and the group must often be recognized merely by Alpha (a) and Beta (P). To the right shines the white light of Spica [416], the first-magnitude star of Virgo [415]. Its recognition will be made even easier for us by the diagram on p. 26. Below CoRVus, the Raven, or Crow [135], stretches the long line of Hydra [210], the Water-Snake, the whale length of which is shown on p. 49. Below the tail of Hydra, very low in the sky near the center of our present map, are a few of the stars of Centaurus, the Centaur [90], one of the great constellations of the far southern skies. Theta (9) is the only one of its brighter stars that can be seen from our latitudes. Very high up shines Arcturus [41], the superb first- magnitude star of Bootes, the Herdsman. To the left is the pretty group called Corona, or Corona Borealis, the Northern Crown [130]. Farther still to eastward, or to the left, lie Hercules [200], and Lyra, the Lyre [260]; and lower down lies Aquila, the Eagle [20], marked by the three stars in a row — Alpha (o) or Altair [21], and Beta (P) and Gamma (7). These are now about at position A as shown in the diagram on p. 28. Through the evening hours of the summer and autumn these three stars, which I have ventured to call " the shaft of Altair," form one of the finest landmarks of the sky. In study- ing Bootes and Hercules the reader should turn to what has already been said on p. 42 and p. 46. Both are very high at the present hour, yet their figures are quite distinct. Below Hercules and above Scorpio there lies, however, one of the most difficult of the con- stellation outlines, Ophiuchus, or the Serpent-Bearer [285], a difficult group. Inability to distinguish this constellation need cause the beginner no discouragement. It has baffled many a veteran. Note the method for learning it §uggested in the Observer's Catalogue [285], but if it is not clear at first, let it await your leisure — learning the other groups first. It should be studied in connection with Serpens, the Serpent [365], which lies on each side of it, the head to the observer's right, the tail to the left. To the right of Arcturus, lies the scattered cluster of faint stars. Coma Berenices, or Berenice's Hair [120]; and still lower toward the west are the stars of Leo, the Lion [225], — but with the familiar "sickle" turned downward more directly than here shown, with Beta (P) or Deneb'ola higher up. Regulus [226] makes with Spica and Antares a fairly straight ine at almost equidistant spaces. The track of the planets, see p. 80, lies here through the constellations Leo, Virgo, Libra, ScoRPius, and Sagittarius, the Archer [340]. The. last is, as yet, hardly above the horizon, but the group is here outlined for observers who at a slightly later time may wish to trace its connection with Scorpio; see para- graph 10, p. 31. Under the next map of the sky to the south it will receive fuller discussion; p. 56. Jfor ®pera»»(BIa96, jficlb^CIass, anb telescope 53 KEY-MAP TO THE SKY AS THE OBSERVER FACES SOUTH. JULY 1, 8 P.M., JUNE 16, 9 P.M., JUNE 1, 10 P.M., MAY 15, 11 P.M., MAY 1, 12 P.M. FOR NIGHT-CHART TO THIS MAP SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES NORTH, SEE PP. 50, 5I. For the sky at other Dates and Hours see Time Schedule, p. 35. The Telescopic Objects. For the Constellations See the Page Opposite. The numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. 1 16. I. With opera-glass or field-glass first note the interesting regions of Scorpio, following the Scorpion's tail from his heart at Alpha (a) or Antares [351] to Tau (t), and through Epsilon («) and Nu (v), round to the end at Lambda (X). This is one of the rich sections of the Milky Way. The httle star Mu (|») [359] in Scorpio is an easy and pretty double, though there is probably no real connection between the components; see p. 13. A field-glass will also indicate the delicate glimmer of the clusters marked M 80 [355], M 6 [356], and M 7 [357], provided the night be clear and the horizon unburdened by mist or fog. The same may be said of the clusters in Sagittarius, the Archer [340], as soon as the fields of this constellation rise — a little later — into better position for observation. The easiest of these are IVf 8 [341] and M 24 [345]. Amon^ the double stars that may be divided by a field-glass, steadily held, are the Alpha (a) [246] of Libra, the Tau (t) [228] of Leo, and the Nu (v) [353] of Scorpio. The last is the small star, unmarked, just to the left, or east, of Beta (P). With opera-glass or field-glass do not fail to sweep through the fine scattered cluster called Coma Berenices, or Berenice's Hair [120], lying just above a line connecting Arctdros and the Beta (pi of Leo. Trace out, also, the pretty figure of Corona, the Crown [130]. There is a cluster of 8th magnitude stars near to Beta (P) in Ophiuchus [288]. II. With a tw^o-inch telescope, examine, first, the objects already noted; especially the Alpha (a) [246] of Libra, and the double stars of Scorpio, Beta (P) [352], Nu (v) [353], and Mu (|i.) [359]. These are all extremely easy and yet none the less interesting. In the case of Nu (v) [353], it is worth while to remember that each of the two components is itself a double star when viewed in a very large telescope. In addition to the above try Sigma (o-)' [358]; and Xi (?) [354], above Beta (P) in the same constellation; Delta (8) [136] in CORVUS; the Gam- ma (y) [417] in Virgo; and the Gamma (7) [227] in Leo. For the last, see also the text under the northward map for this same hour; p. 51. Turning eastward, or to the left, try the stars marked (57 [286] and 70 [287] in Ophiuchus — the former is the easier; and Theta (9) [368] in Serpens. The last named star is not easily found when so low in the sky, but we may note that it lies to our left from Ophiuchus, just to one side of a line connecting the Zeta (t) and Lambda (X) of Aquila. You will see from the Night-Chart that each of these guide stars is one of an obvious pair. Another method for finding our object is noted in the Observer's Catalogue. Space has been given to such directions because the Theta (9) [368] of Serpens is of unusual charm and beauty. III. With a three-inch telescope and with instru- ments larger than a three-inch the objects already named should first have careful examination. To these may be added the Alpha (a) [416], Theta (9) [418], and Tau (t) [419] of Virgo; the Iota (i) [248] of Libra; the Xi (I) [251] of Lupus, just below Scorpio; the Alpha (a) [201] of Hercules, a superb object; and — in the same constellation — the stars marked Mu (p.) [203], p5 [205], Gamma (7) [208], and Rho (p) [204]. Try also the Zeta (?) [131] of Corona; and the Mu (p) [47], Delta (8) [43], Xi (S) [43 b]. Pi (w) [44], and Epsilon («) [42] of Bootes. The last named star is a fine object but difiicult except in a larger telescope. A number of the stars just mentioned are so easy as to be properly objects for a two-inch, but they are now so high that an instrument of larger aper- ture, with a low-power eye-piece, will find them more readily and permit a more satisfactory view of them. View also with such an eye-piece the clusters and nebute M 17 [344], M 20 [342], and M 22 [343] in Sagittarius, as well as those already mentioned. The cluster M 5 [371] in Serpens forms an equilateral triangle with Mu (n) and Epsilon («) in that constellation ; or it may be found by a line from Iota (i) to Beta (P) in Libra continued onward a like distance. a 36eainner'0 Star*36ooh NIGHT-CHART TO THE SKY AS THE OBSERVER FACES NORTH. SEPT. 1, 8 P.M., AUG. 15, 9 P.M., AUG. 1, 10 P.M.. JULY IS, 11 P.M., JULY 1, 12 P.M. FOR KEY-MAP TO THIS CHART SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES SOUTH, SEE PP. 56, 57. For the sky :it other Dates and Hours see Time Schedule, p. 35. The Constellations. For the Telescopic Objects See the Page Opposite. The numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. Ii6. As we face toward the north, we find that the Great Dipper, in its revolution round the Pole, is at our left, rather low, with the bowl of the Dipper turned eastward. If we turn to the diagram on p. 23, we may see that the Dipper is proceeding now from position D to position A, its stars Beta (P) and Alpha (a) still pointing, however, to Polaris, the Pole-Star [406]. Ursa Major, or the Great Bear [400], of which the Great Dipper is the only conspicuous part, is supposed to have his nose at Omicron (o), his ears at Sigma (), Sigma (). One object, at least, is clearly and prettily marked, — the mouth of the Water Jar, formed by the little Y-shaped figure at Pi (it), Eta (1), and Gamma (7). In the lines of faint stars running downward through Phi (<|>) and Omega (a), and onward, some have seen the trickling of a jewelled stream into the mouth of the Southern Fish, Piscis AusTRiNus [330]; — for the mouth of the Fish iS marked by FoMALHAUT [331], a fine first-magnitude star. At this hour, precisely, Fomalhaut is not yet quite above the horizon in our northern latitudes. Northward from Aquarius, the great square of Pega- sus, the Winged Horse [301], is now apparent. As Pegasus is so great in size and as it is divided between the south and north, the text and maps here should be supplemented by those on pp. 54, 55. The shoulders and body of the horse are represented by the "square"; the head is toward the south, at the sta^s Zeta (I), Theta (6), and Epsilon (e); and the forefeet are at Eta (tj) and Kappa (k). The huge animal has, therefore, his back toward the horizon, his feet in air. The"square" is formed only by including the Alpha (o) of Andromeda, as explained under the preceding Night Chart; and the explanation of the distortion there, is applicable here. Turning again to the south, we see that the stars of Scorpius, or Scorpio [350], are sinking toward the west, but the fan-shaped figure made by the six bright stars — Antares [35x1, Tau (t) and Sigma (), and feet about at Omega (u). The present position of the body is thus almost parallel to the horizon. Above Aquarius is Pegasus, the Winged Horse [301], the head represented by the obtuse triangle, Zeta (t), Theta (9), Epsilon (t); and the forefeet by the stars Beta (P), Eta (i\). Pi (ir); and Lambda (X.) to Kappa (k). The shoulders and body are represented by the "great square," the stars Alpha (a), Gamma (7), and Beta (P) of Pegasus and the Alpha (a) of Andromeda. As is the case with many of the constellations, the figure is not complete. From the square of Pegasus, Andromeda [i] stretches in an almost straight line; see p. 54. Lower down are Triangulum, the Triangle [395]; Aries, the Ram [30); and Pisces, the Fishes [320] — not to be confused with Piscis Austrinus of which we have already spoken. The stars of Pisces are faint, but an imaginary line from Alpha (o) to Beta (P) in Aries, if continued onward, will cross the two lines of stars which meet at a point and form the eastern end of the constellation. Farther toward the west, or to the right, the other termination of the group is formed by the pretty chaplet of stars at Theta (8), Lambda (\), Gamma (7), etc. Many of these stars are too faint, except on very clear nights, to be seen without an opera-glass. Alpha (a) is the brightest object of the constellation. In some of the ancient atlases the stars from Alpha (a) to Eta (tj), etc., marked the "Eastern" Fish, those at the chaplet the " Western" Fish, and the stars from Mu {}>■) to Omega (») represented a ribbon or garland binding them together. Near the Alpha (o) of Pisces lies the head of the huge constellation called Cetus, the Whale [no]. The creature's head is formed by the stars Alpha (a) , Lambda (X), Mu (|jl). Gamma (7), etc., and his great tail stretches downward and westward to Beta (P). We have already noted the first-magnitude star Fomalhaut [331] — directly to the south. A little to the west, and just above, is the constellation Capricor- nus, the Sea-Goat [75], with stars so faint as to be almost invisible except upon a clear night.' We may always find its location, see p. 28, by remembering that the "shaft of Altair" — the three stars. Alpha (o), Beta (P), and Gamma (7) of Aquila [20] — points downward directly to it, just as it points upward in the general direction of Lyra, the Lyre [260]. We have already spoken of Sagittarius [340], on p. 56. Above Altair, as it sinks to westward, we find the small constellations, Delphinus, the Dolphin [155], and Sagitta, the Arrow [335]; and higher, and farther to the north, is Cygnus, the Swan [145], marking the Northern Cross. But, as shown on p. 28, the shaft of Altair — the three stars Alpha (o). Beta (P), and Gamma (7) in Aquila — ■does not point so directly downward as shown above; it now lies more nearly parallel to the horizon. Upon the other hand, the Northern Cross and Sagitta do point downward more directly. Of Lyra [260] we have just spoken, p. 58, under our northward map. The remaining constellations toward the west are now too low in the sky for clear observation. The track of the planets lies in our present map through Sagittarius, Capricornus, Aquarius, Pisces, Aries, and Taurus; see p. 80. At precisely this hour, in northern latitudes, the first of these has set; see note 10, p. 31. ]for ®pera*(5lass, Jfielt)^(51as0, anb telescope 6i KEY-MAP TO THE SKY AS THE OBSERVER FACES SOUTH. NOV. 1, 8 P.M., OCT. 15, 9 P.M., OCT. 1, 10 P.M., SEPT. IS, 11 P.M., SEPT. 1, 12 P.M. FOR NIGHT-CHART TO THIS MAP SEE OPPOSITE PAGE. FOR THE SKY AS THE OBSERVER FACES NORTH, SEE PP. 58, 59. For the sky at other Dates and Hours see Time Schedule, p. 35. The Telescopic Objects. For the Constellations See the Page Opposite. The numbers in brackets [ ] refer to corresponding numbered notes in Observer's Catalogue, p. ii6. I. With opera-glass or field-glass first examine the course of the Milky Way, lying here to the westward, at the right, and running from Cygnus at the northwest, southward through Sagitta, Aquila, and Sagittarius. It will be interesting, also, to trace out the pretty chaplet of small stars formed b^lTheta (6), Gamma (y), Lambda (X), etc., in Pisces. It is now almost due south, upward and a little to the left from the bright star Fomalhaut. Trace, also, just to the right of this pretty figure, the little Y in Aquarius, which forms the mouth of the water jar. Among the double stars that may be divided by an opera-glass or field-glass are Alpha (o) [76] and Beta (P) [77] in Capricornus; and also the star marked 6 [426] near the foot of the Cross in Cygnus. Of the easier double stars in Lyra, and of the Pleiades in Taurus, we have spoken on p. 59, in connection with the northward sky. Among the smaller groups here before us, Del- PHiNus and Sagitta will be found of special interest. . II. With a two-inch telescope first note, with eye-piece of lowest power, the objects already mentioned. Sweep through the rich sections of the Milky Way, especially in the neighborhood of Altair [21] and down- ward toward the west, past the Lambda (X.) of Aquila and the Lambda (X) of Sagittarius. Among the double stars there is a fine object for a two-inch telescope in the Beta (P) [332] of Piscis Aus- TRINUS, low down but now almost directly before us to the south. An easy and beautiful double is the Gamma (7) [157] of Delphinus; and even finer is the Beta (P) {147] of Cygnus. But of this, and of the stars in Lyra, we have just spoken on p. 59. Turning now to the east, or toward the left, beautiful objects are to be found in the Gamma (7) [32] and Lambda (X) [31] of Aries, and in the Pi (ir) [4I and the Gamma (7) [3] of Andromeda, — though the latter are rather high for convenient study. Among the faint stars of Pisces we may try Alpha (a) [321] and Psi (» iW SATURN From Photograph by Dr. Percival Lowell, Lowell Observa- tory, Flagstaff, Arizona HALLEY'S COMET, MAY 5, 1910 From a photograph taken at the Yerkes Observatory 92 Comets an& flDeteors 93 with great rapidity, completing its revolution in lo hours, 14 minutes (the day of Saturn), the great ball is "bulged out" or broadened at the equator and flattened at the poles. This oblateness of the sphere is even more marked than in the case of Jupiter. A small telescope will show it. Comets and Meteors There is no weighty reason why any amateur astronomer should not be the discoverer of a comet. The requisites are a telescope of low power, large field, and generous illumination ; a good store of pertinacity and patience; and a fair knowledge of the constellations — in order that the observer, by reference to the neighboring stars, may be enabled to decide as to the fact of motion in a suspected object. If, after several hours, no motion — in reference to surrounding stars — be noted, the probabilities are that the object is not a comet but a nebtila. For almost all comets, especially on our first view of them, look much like nebulae, having the appearance of small patches of mist. These may never grow much brighter, may never show nucleus or tail, and may bring not much of fame or pride to the discoverer. But the essential characteristic of a comet may have been found. This is the coma, the misty cloud of faintly luminous material of which we have been speaking. The essential thing is not a "tail" nor even the nucleus (the bright core, or point almost starlike in its brilliance, at the centre of the coma) but the coma itself. As we look at the illustrations of a comet we naturally think of it as rushing through space with its tail streaming out behind it just as a flame of fire streams backward from a hurtling torch. The tail of the comet, however, sometimes goes before it. In fact, the tail (if there be a tail) always extends from the comet in the direction opposite to the Sun, — so that as a comet approaches the Sun the head precedes the tail, but as it leaves the region of the Sun the tail precedes the head. Through causes which no one has yet fully explained, the Sun, while powerfully attracting the comet as a whole, seems to exert a repulsive force upon the infinitely refined material of which the tail is formed. The head or coma of a normal comet is frequently as much as 100,000 miles in diameter. Many are far larger. The tail ranges in length from 10,000,000 to 100,000,000 miles; the diameter of the nucleus, or bright point within the head, is from 100 to 5000 miles. Astronomers differ as to the nature of the stuff or matter of which the nucleus is composed. Some have supposed this matter to be made up of swarms of meteors, — or extremely small particles, widely separated, glowing with an incandescent heat resulting from collisions with one another, or luminous from some form of electrical action. No positive knowledge is yet at hand. We do know, however, that the stuff or matter of a comet is, on the whole, of almost inconceivable rarity or tenuity, so thin and impalpable that probably no harm to us could result from any possible collision with such a body. Comets which have closed orbits return again, and their return may in many cases be p;-edicted. Among these are Encke's, with a period of 3^^ years; Swift's, with a period of 5M years; Tuttle's, with a period of 13^ years; and Halley's, with a period of 76 years. The last named is the most famous because it was the first to have its return predicted and the first to indicate the feasibility of such calculations. Many of the noblest comets of history have not been again identified, either because their orbits are not closed — ^bearing them forever beyond owe solar system — or because, though closed, their orbits are so vast as to permit their return only after hundreds or even thousands of years. Our illustrations 94 a Beginner's Star»»Booft are chiefly from photographs of Halley's Comet taken at its recent return. It has returned periodically for many centuries, sharing intimately in some of the critical occasions of history, as in the Norman Conquest, A.D. 1066. The opening scenes of Tennyson's drama, Harold, contain some striking and significant references to the strange visitor. For while COMET MOREHOUSE, 1908 Photographs from the Yerkes Observatory ; taken three hours apart we now know that comets are altogether harmless to our Earth, they were often supposed by the ancients to be the forerunners of calamity if not the symbols of divine displeasure. In noting our photographs of the comets, see p. 29 as well as pp. 92, 95, 137, the reader should give no regard to the light-streaks that appear on the photographic plate. These are traces of the stars. The camera must be adjusted to follow the comet. If the exposure must be a long one, as is usually the case, the apparent movement of stars is not likely to be at either the same angle or at the same velocity as that of the comet, and the traces of the star-images must appear upon the plate. Several types of comets are shown. That of Giacobini, p. 29, was remarkable for the large relative size and impressive form of its head ; that of Morehouse, above, for the relative smallness of the head and the peculiar form and striking changes of the tail. Of meteors there is little to be said in a volume such as this, because they are of small telescopic interest. They are not, of course, real shooting "stars," for they are relatively very small and they live and perish within our solar system. They "rain a ceaseless rain" upon the Earth. Nor do they fall at random out of space, as was once thought. They revolve, apparently in swarms, in orbits about the Sun, — some speeding in the same direc- tion as the planets, some with motions that are retrograde, and some in orbits that cross our own. So rapidly do they move that they enter our atmosphere with a velocity which by the force of its impact with the air raises them to a heat of inconceivable intensity. The smaller bodies shine for a moment or two and are consumed; the larger fall, and when HEAD OF HALLEY*S COMET, MAY 8, 1910 Reduced from Photograph taken at the Mt. Wilson Solar Observatory See also pp. Q2 and 137 95 96 a Beainner'0 Star^Booft picked up are called meteorites and aerolites. From about July 20tli to Aug. i6th (maximum of display Aug. nth) the earth passes through a swarm of meteors which seem to radiate from the direction of the constellation Perseus. They are therefore called "the Perseids. " In November, about the 15th, we meet the Leonids, coming from the apparent direction of Leo. The Geminids (Gemini) are seen about December 7th and for some days there- after. November 24th is the date for the Andromedes; October 19th, for the Orionids; May 6th, for those coming from the region of the star Eta (7) in Aquarius; July 28th, for those coming from the region of Delta (S) in Aquarius ; April 20th, for those coming from the region of Lyra. In counting them, an opera-glass or a field-glass of low power is some- times useful, especially in noting those with the lower velocities. The three important points to be noted are the number per hour, and the duration and direction of their flight. In fixing the direction in the observer's memory, a cane or wand instantly held in line with the meteor's flight has often proved a convenience. That meteors are the fragmentary masses of former, or still existent, comets is now the generally accepted theory of their origin. Fuller information as to both classes of objects may be had in the general volumes on astronomy mentioned on p. 144, — especially in those by Sir Norman Lockyer and Miss Agnes M. Gierke. See, also, p. 143 of this volume under the head of "Useful Work for the Amateur." "On a starred night Prince Lucifer uprose. Tired of his dark dominion swung the fiend Above the rolling ball in cloud part screened, Where sinners hugged their spectre of repose. Poor prey to his hot fit of pride were those. And now upon his western wing he leaned. Now his huge bulk o'er Afric's sands careened, Now the black planet shadowed Arctic snows. Soaring through wider zones that pricked his scars With memory of the old revolt from Awe, He reached a middle height, and at the stars. Which are the brain of heaven, he looked, and sank. Around the ancient track marched, rank on rank, The army of unalterable law." George Meredith: Lucifer in Starlight. IDH. Some llnstruments of ©bservatlon The Opera-Glass and Field-Glass Said a distinguished astronomer, the late R. A. Proctor: "I have often seen with pleasure the surprise with which the performance even of an opera-glass, well steadied, and directed towards certain parts of the heavens, has been witnessed by those who have supposed that nothing but an expen- >''^S^^*V ^' ' -w^ sive and colossal telescope could afford any ^^^?5S-^B W^^SS^^ views of interest. But a well- constructed ■HHMHBtfB^^^B^BlHHl^r achromatic telescope of two or three B^ B 1|^^b9V inches in aperture will not only supply ^B ^^B_— ^^^^^_^^B J^^K amusement and instruction; it may be I^^^Ji^l^^^^^P^^^^^^l^lv made to do useful work."* Such a state- mg^^^^m^ ^^^^^^ ^K^^^»0 ment even more applicable to-day than ^^^^^^^^ ^^^^^H ^^^^^^^H when Proctor wrote Not only are our ^^^^^^^^^^^^^T ^^^^^^^^^ small telescopes better in quality, but the ^^Bs^^^^^^ ^H ^^HjHj^lA modern opera-glass and field-glass are more ^^H^^^^^^^^^^^^^^^h^Sh^^H to astronomic ^^^^^^^^^^^^^g^^^^^^^^^^^^B The opera-glass is not, as is sometimes ^^^9^^^^^^^ ^^^^^^^^^^ supposed, either a plaything or a toy. It is ^^^^^^^^^ ^^m^^^^^ a serious instrument. While it cannot do * modern opera-glass the work of a great telescope, it can do some things for which the great telescope is unfitted. We may remember the retort of the squirrel to the mountain, in Emerson's quaint poem: "If I cannot carry forests on my back, neither can you crack a nut!" The opera-glass, because small in size, maybe slipped easily into the pocket; and, because light in weight, may be handled and used for long periods without fatigue. With it one may catch the view of a meteor's trail more quickly than with a heavier instru- ment. It can be always ready. Because its magnifying power is not high, it is less easily affected than the telescope by fogs and mists; and, for the same reasons, its use is more practicable in travel, — as on shipboard or on a moving train. Moreover, its magni- fying power is quite sufficient to be of frequent aid in following a comet, in studying brilliant star-fields like those found in the Pleiades and in Orion; and it is of special value in helping the amateur observer to trace the outlines of the constellations. Even after the telescope has been adopted and is well understood, an opera-glass is often of definite service in examining unfamiliar star-fields — especially upon dull or hazy nights — ■ in order that the larger instrument may be intelligently directed. As with all optical products these vary in quality. There are opera-glasses and opera- * Half Hours with the Telescope, by R. A. Proctor, M.A., F.R.A.S.; p. i; Longmans, Green & Co., New York and London, 1868. 97 98 a Beginner's Star^Booft glasses. Often the same glass that has been used for years at the theatre is also quite satisfactory for the study of the stars. The best for this purpose are undoubtedly those having large object lenses, — the object lenses are at the end nearest the object viewed; or, in other words, the lenses at the large end of the instrument. The larger these are— other things being equal — the larger will be their light-collecting power. Magni- fying power is not so important in such a glass as its power to show a fairly large field brightly and clearly lighted. The beginner should be constantly on guard against the temptation to exaggerate the impor- tance of mere magnifying power. I cannot concur in the opinion sometimes expressed that it is wise, in purchasing an opera-glass, to go to odd and out-of-the-way places to field-glass: prism binocular type secure one. There are doubtless excellent glasses to be found in some of these shops. But in going to a regular dealer you may not only be reasonably sure your glass is what it is represented to be, but you are dealing with one who will have a permanent interest in its quality and service. Excellent glasses may be had of the regular dealers at very moderate prices, ranging from $4 or $5 to $15 or $20 a pair. The optical principles represented in the opera-glass involve, however, certain limi- tations as to power. Some glasses magnify but 2Y2 diameters, some magnify 3, some 33^ or 4. But the greater the magnifying power the greater in length must be the tubes or cylinders of the instrument. The ordinary field-glass is, accordingly, but an opera-glass of greater length ; and because the principle of construction is the same as that employed by Galileo in his earliest models of the telescope, such an instrument is said to be of the "Galilean" type. The Galilean field-glass has greater magnifying power than the opera- glass; and, if well made, will present images or pictures of great sharpness and clearness. But in some of these instruments the picture is not well lighted or sharply defined except at the very centre of the field of view ; the field of view is small, at best ; and the physical weight of glasses of this type is quite large for the magnifying power afforded. When, therefore, a magnifying power of 7 or 8 diameters is attempted the GaHlean field-glass usually becomes too large and bulky for comfortable use. There is, however, one modern improvement much to be commended to the purchaser who can afford it. This is the device for permitting the adjustment of the glass to vary- ing pupillary distances. The eyes are not the same distance apart in all heads, and these "jointed bars" permit the comfortable adaptation of the field-glass to the individual. Where the "jointed bars" cannot be obtained and the frame is therefore rigid, be sure to select your glass so that it is suited to the distance between your own eyes. This can be easily tested by noting whether the two tubes of the glass present a single field of view. The two miniature telescopes of which the field-glass is composed should do good "team- work." They should show one picture. It is well to select the plainest, simplest "finish" as the most desirable, especially for outdoor use; and if the instrument be that of one of the better manufacturers it will more than justify the amount expended in its purchase. Ilnstruments of ©bservation The Prism Binocular 99 By the invention, however, of the prism binocular, another type of field-glass is now available. A new principle has been brought into play. Some sixty years ago a French engineer named Porro discovered that through the introduc- tion of highly polished glass prisms, at the proper intervals within the tubes, the rays of light could be so "doubled back" upon themselves that the optical necessity for the increased length demanded by increased power could be elimi- nated. High powers could thus be provided for, through tubes that might be actually very short. This ingenious sug- gestion has now been so broadly adopted that there are many kinds of "prism binoculars," several of the different "makes" representing a high degree of optical refinement. They are naturally more expensive in price than glasses of the Galilean type. The fitting and polishing of the prisms, and the very rigid mechanical construction demanded in the body of the instrument, require workmanship of rare experi- ence and skill. The Galilean field-glass ranges in price at retail from $io to $20; the better grades of prism binocular range from $40 to $75, — though there are some as low as $25 and some as high as $90. Much depends upon the precise model desired. As in the case of the opera-glass, the best types for astronomical purposes (costing from $40 to $75) are those possessing large object lenses. The large object lenses, as already explained, ensure for the instrument a large light-collecting capacity. This increases the pleasure in its use at night and also gives it a high penetrating power under adverse conditions of light and air. Not only are these instruments smaller, in proportion to their magnifying power, than the Galilean glass, but they present a large field of view, well defined, and clearly and evenly lighted to the very edge of the picture. The optical conditions, however, which result in the relative reduction of both light and field with the increase in magnifying power are inexorable, and apply here also in spite of the superiority of the prism binocular to the GaUlean glass. Because of these conditions it is not wise to select, even in a prism binocu- lar, a power in excess of 6 or 7 or 8 diameters if the instrument is to be given "free-hand" use, — is to be used without some form of artificial support. For we must also bear in mind the fact that just as your field-glass magnifies the objects to which you direct it, it must also magnify — and precisely to the same extent — the trembling or unsteadiness of the directing hand. The higher the magnifying power you employ the more difficult you will find it to hold your instrument "steady," — unless you use some form of artificial support. The various magnifying powers — as 6X, 7X, 8X, 9X — are usually specified upon the frame or body of the glass. The symbol X means "times" and represents the times an object is magnified, or the extent to which the apparent diameter of an object is increased. In the same way we say that a glass or telescope has a power of 8 or 15 or 100 diameters. This means that the instrument increases to this extent the apparent diameter of the object. Where, however, some form of artificial support for the glass can be purchased or devised, H[GH POWER, PRISM BINOCULAR, FIELD-GLASS On Tripod Support 100 E Beginner's Star^Booh much satisfaction can be found in powers as high as lo, 12, 15, or even 18. Prism binoculars may be had in all these magnifications and if care be taken to select a model having large object lenses, and thus affording abundant light, such a glass has some advantages over the small telescope. Among these advantages we cannot include economy, for they are more expensive than some telescopes, ranging in price from $60 to $90. They do, however, afford the pleasure and comfort of "binocular" as opposed to "monocular" vision; that is to say, we may use both eyes naturally and easily in looking through them. A power under 20 diameters, however, will not show the ring formation of Saturn, or many of the double stars. But such a glass, even if it have only a power of 10, will divide a few of the double stars, will show the four larger satellites of Jupiter, the crescent phase of Venus, and beautiful views of the more conspicuous features on the surface of our own moon. Metal holders or clamps may be purchased of almost any optician, either with an accompanying metal support, or to be used in adjusting the glass to any ordinary camera tripod. The large object lenses provided with instruments of this type make them especially useful in looking for comets or in viewing brilliant star-groups such as the Pleiades. The Spy-Glass or Draw-Telescope This familiar glass, the ordinary hand telescope of the mariner and the hunter, affords neither the comfort of "binocular" vision nor the high magnifying power of the regular astronomical instrument, but it is inexpensive and it will often do good work. For views of the wider double stars, for the coarser star-clusters, and for the study of our own moon and of the four larger moons of Jupiter, such telescopes are usually quite adequate. Their eyepieces present an "erected" image — a term we will explain a little later on — and so their objects in the field of view are "right-side-up," as in an opera-glass or a field-glass, but this field of view is small and not well lighted. Unfortunately the eyepieces furnished with them are often of higher magnifying power than the size of the object lens and the construction of the instrument will justify, but the manufacturers are gradually correct- ing this error. There has been prevalent a natural but thoroughly unintelligent demand on the part of the public for "high" magnifying powers in all of our popular field-glasses and telescopes. Manufacturers long felt that they must yield to this demand, though they knew it to be self-destructive (a magnifying power so high as to compromise the pleasure-giving quality of the telescope is "bad business" commercially as well as astro- nomically) but happily a change is now at hand. In using a spy-glass, or hand telescope, remember that to do any sort of satisfactory work it must be steadily held. The metal clamps used for fixing a field-glass to a tripod are just as well adapted to the spy-glass. If these are thought to be too expensive, the amateur who possesses a little skill at wood-working can make his own mounting, at very low cost and with small trouble. A forked staff set in the ground, the telescope resting in the fork, is better than nothing. At the section of the telescope at which the instrument is grasped by the metal clamp or by the fork a piece of soft cloth or chamois-skin should be wrapped about the tube, to prevent its polish from being injured. This piece of soft leather or cloth may be held by a few stitches or by a couple of tight rubber bands. This type of telescope is usually made in sections or joints, the smaller sliding down into the larger when the instrument is closed. The instrument must, of course, be extended or drawn out for use in observation — hence the name "draw-telescope" is often applied to it. A three-draw telescope or a four-draw telescope is one having three or four, as the case may be, of these several sections. The focusing is accomplished by sliding in or out the ■flnstruments of ©bservatlon loi section containing the eyepiece. Telescopes of this type will not, of course, give the satisfaction afforded by instruments regularly mounted on tripod stands and provided with one or more regular astronomical eyepieces, but they are inexpensive, easily carried about, and capable — within their range — of giving a great deal of pleasure to the beginner. Their prices range from $5 to $50 according to quality and size. The Astronomical Telescope Portable telescopes mechanically mounted on tripod stands may be had in almost any size from an "aperture" of i3^ inches to 5 inches. The "aperture" (literally = opening, or space through which Hght passes) of a telescope represents the surface diameter of the object lens, or the "objective." The object lens or objective of the telescope, as already explained, is at the large end; the lens at the small end is called the "ocular" or sometimes — in a general sense — the eyepiece. The size of the telescope is usually described in terms of the objective, — a "2 -inch" is a telescope with the objective 2 inches in diameter; a "3-inch" is a telescope having an object lens 3 inches in diameter, etc. Telescopes are also classified as to type or kind as "reflectors" and "refractors." The reflectors are the better for such work as astronomical photography ; the refractor is the type found in most general use, especially among amateur observers. Moreover, the greater achieve- ments in observation have been thus far accomplished by instruments of this kind. The famous 36-inch telescope of the Lick Observatory and the 40-inch telescope of the Yerkes Observatory are both refractors. This book deals exclusively with the using of small refractors, inasmuch as this is the type of instrument found in the stock of the average optician and used in practical work by the larger number of observers ; — but those posses- sing reflectors will find the directions and instructions easily adapted to their instruments. A telescope has but one objective or object lens, but it may have several eyepieces. One eyepiece may be removed to make place for another; the object lens, however, should never be removed, except at long intervals for cleaning : we will speak below, see note 9, p. 11 1 , of the proper cleaning of lenses. If you find a few small "bubbles" in the glass of the objective these need cause you no concern. They are often found in glass of the highest quality, and — unless present in large numbers — they will not affect the optical qualities of any telescope that is in other respects a good one. The telescopes of well-known makers are, as a rule, carefully tested before leaving the factory, for a poor instrument is a poor advertisement. The beginner may usually be sure, therefore, that his telescope is all right. Suggestions for the testing of objectives are found in some volumes, but one who is using a telescope for the first time is seldom able to apply these instructions successfully. They have often caused more anxiety than aid. Upon the other hand, helpful advice may often be had from observers of larger experience. There is a fine esprit de corps among amateur astronomers and those who have met and solved their telescope-problems are usually glad to be of service to those who are entering the fellowship. Yet it is true that the user of a telescope is more or less bored by such enquiries as "How far can you see with it?" One may well retort, "I can see no farther with it than without it!" — ^for in beholding some of the brighter stars with the unaided eyes we are seeing to the Umit of mental comprehension, — a distance which if stated in English miles could not be expressed in twenty million consecutive human lifetimes, if every breath of each were to represent a mile. The value of a telescope cannot be expressed in terms of the linear distance which it can penetrate. Nor can it be well expressed in the terms of mere magnifying power, for the highest magnifying power optically possible to it may 102 a Beginner's Star=3l5ooft be — because of the conditions of the atmosphere or the limitations of the eye — altogether useless from a practical standpoint. What, then, does a telescope do for us? It does have both a penetrating and a magnifying power, but its chief function is the collecting of light for the eye, — illumination. No amount of magnifying will prove of service to us if the mere enlargement of the size of the image is not coincident with its adequate illumination in the field of view. And in the case of the stellar world, the distance of which is optically and practically at infinity, the illumination of the field of view is the chief function of tele- scopic aid. I here make no reference to the telescope scientifically mounted as an instnunent of precision for the measuring of angles, etc. I refer to the telescope in average hands. The observer in attempting to see and to study the familiar objects of astronomic interest is constantly forced to realize that merely increasing the size of an image may actu- ally prevent his seeing it, for the increase in magnifying power necessarily involves not only the reduction of the size of the field of view but the proportionate shutting out of the light needed for its study. Let us therefore first try to appreciate the telescope's light- collecting power. This is proportionate, as we have seen, to the size of the object glass. The diameter of the eye's pupil is about \ of an inch; and working with the formula that "the light-gathering powers of the eye and the telescope are to each other as the squares of their apertures" we find that a 2-inch object glass will gather lOO times more light than the natural eye. To get the light-collecting power of an object lens as compared with the eye, we thus divide the square of the diameter of the lens by the square of -I-; or we may merely take the number 25 and multiply this number by the square of the diameter. Thus, a 3-inch objective will collect 225 times as much light (9X25) as the unaided eye; the 4-inch telescope will collect 400 times as much (16X25), etc. A 3-inch objective thus gives more than twice as much light as a 2-inch, and a 4-inch nearly twice as much as a 3-inch. The object lens, receiving its normal share of light,. and receiving with it an image from without, sends both down the tube of the telescope to be received by the eyepiece. The amount of light, while generous, is fixed in quantity. But the image, upon the eye, is not yet fixed in size; it can be varied in size by the different magnifying powers rep- resented in the different oculars. If the power of the eyepiece be great the light received must be spread over a large image and the impression must be dim ; if the power be small the light is not so much spread out, or diffused; and, as the parts or factors of the image lie closer together, the light may fall upon the whole with more of concentration. The re- sulting image is smaller but brighter. It is thus that low magnifying powers involve a relative intensity of illumination, and high magnifying powers involve a relative diffusion, or loss, of light. This is not the whole story. Questions of optical theory lie outside the prov- ince of this book. It is well, however, for the beginner to appreciate a few of the reasons why, as I have said, the attempt to increase the size of an image in a particular telescope may actually prevent our seeing it. The practical astronomer has always laid stress, therefore, upon the maxim that "the highest power which can be used with advantage is the lowest power which will show the object. " In other words, if a power of 50 will show you the thing for which you seek, there is no gain and much loss in crowding on a power of 75 or 100. The Astronomical or Reversing Eyepiece Practically all telescopes of standard quality are provided with two or more astronomical eyepieces. They are usually provided also with a terrestrial eyepiece for viewing ob- jects on land or sea by daylight. This latter is in the longer of the sliding tubes that slip in and out of the main body of the instrument. Removing this tube with its eyepiece, Ilnstruments of ©beervation 103 the shorter tube may be slipped into its place. This shorter tube carries the astronomical eyepieces; they may be slipped or screwed into it, and are interchangeable. Upon each a cap of dark-colored glass is sometimes found. This is for use in viewing the Sun (see, however, par. 2, p. 64) and shotild be removed, of course, when viewing other objects. First learn to focus with the astronomical eyepieces by daylight, directing the tele- scope to some distant object, preferably on land rather than at sea. Begin with the eyepiece of lowest power. On looking through it the beginner will note that the image is inverted, or "upside-down." This is no reason for indignantly return- ing the telescope to the dealer as defective, — a course that has been followed more than once. All astronomical eyepieces show an inverted image. The image is so presented by the object lens. It reaches the eyepiece upside- down. It is a simple matter to erect it, if we so desire. This is done, indeed, by the terrestrial eyepiece, for by dayUght, and in viewing objects upon the earth, it is confusing and disconcerting to have to view them upside-down. But in the sky, where there is no scene of closely related objects to which we must mentally adjust ourselves, an inverted image makes practically no difference to us. We soon grow used to it. And such inconvenience as it may cause is more than offset by the fact that with the image inverted we can enjoy more of the light-collecting power of the telescope. For the erection of the image additional lenses must be used — this is one reason why the terrestrial eyepiece is longer and is more expensive than the astronomical — and these additional lenses for the erection of the image necessarily absorb a portion of the light. We have spoken of the fact that the two or more astronomical eyepieces usually pro- vided with each telescope represent different magnifying powers. But it is well to remem- ber that the magnifying power of the telescope is also determined, in part, by the size of the object lens.* In other words, the result is due to a combination of the lenses at both *Each lens has always a iixed "focal length. " The focal length of a lens represents the linear distance between the centre of the lens and its focus. The magnifying power of a telescope is that of the eyepiece and the object lens in combination; and this power equals the focal length of the objective divided by that of the eyepiece. For example, if the focal length of the objective is 38 inches, and the focal length of the eyepiece is half an inch, the magnifying power of the combination is 38-^0.50 = 76. TELESCOPE — MODEL A All'Azimuth Mounting 104 H ^Beginner's Star*ffiooft ends of the instrument. The objective, however, is fixed; so we secure our changes in magnifying power by changing the eyepieces. And as this is easily and quickly done we fall naturallj' into the habit of speaking of "40-power eyepieces" or "eyepieces of 60 power." This habit is a matter of convenience. It does not become an inconvenience unless we forget the truth of the case in ordering a new eyepiece, and merely send for a "50-power eyepiece." No one will know precisely what eyepiece we wish unless we also specify the size of the object lens, the length of the telescope tube, and — if possible — the name of the maker. For an eyepiece that will give a magnifying power of 50 on a 3-inch telescope, will give less than 50 on a 2-inch and more than 50 on a 4-inch. What Magnifying Powers? In selecting the astronomical eyepieces for a small telescope it is well to have at least two — and, if the purse permit, a third or even a fourth. Two, however, should be regarded as essential, — one a low-power, for easy double stars, for star-clusters, comets, nebulae, general star-fields like the Milky Way, and for all objects presenting an extended image. Here the primary requisites are abundant light and a generous field of view, — conditions afforded by low powers and rendered impossible with high powers. An eyepiece of high power will often prove useful for difficult double stars, and for the study of detail upon Sun, moon, and planets. Between the highest and lowest powers it is well, when feasible, to have an intermediate eyepiece, for use under special conditions that may arise while the observer works. At- mospheric difficulties may make the highest power useless on a night when the planets are of special interest; or a double star, too "close" for the lowest power, may require more light than high magnification will permit. Indeed the intelligent observer will find that one of the most interesting phases of his work will be the adaptation of his instrument, from object to object or from hour to hour, to the immediate conditions with which he deals. No absolutely rigid rules may be imposed. It may be helpful, however, to indicate a series of eyepieces for the sizes of telescopes in popular use. This is here done, distinctly upon the assumption that these suggestions are only approximate and that a variation of a few diameters in any particular case should not be a cause for rejecting a telescope. Indeed, a manufacturer in providing the optical equipment for his instruments may often prove a better judge than any one else. In some cases, however, the manufacturer does not specify the powers of the eyepieces, merely offering a given number (two, or three, or four, etc.) with the instrument, — and leaving it to the purchaser to choose the powers. In such cases, then, these suggestions may prove useful. In selecting astronomical eyepieces the best two powers for a 2-inch telescope would be 25 X and 75 X ; the best three powers would be 25X, 60X, 75X. For a 23^-inch the best two would be 30X, 85X; the best three, 30X, 65X, 85X- For a 2yi-mch the best two, 35 X , 95 X ; the best three, 35 X , 70 X , 95 X . For a 2 ^-inch the best two, 40X, looX; the best three, 40X, 75X, lOoX. For a 3-inch telescope the best two powers would be 45 X and 115 X ; the best three, 45X, 75X, 115X; the best four, 45X, 75X, 115X, 150X. For a 3H-inch the best two, 65X and 160X; the best three, 65X, 95X, 160X; the best four, 65X,95X, 140X, 160X. For a 4-inch telescope the best three, 70 X, 150X, 230 X; the best four, 70 X, 100 X, 150X, 230X; the best five, 70X, looX, 150X, 230X, 285X. The series just outlined might be continued indefinitely; but for other instruments the observer will find it easy to apply the general principles suggested by the examples Unstruments of ©baervation 105 cited. In a number of cases I should have suggested, for the lowest power, eyepieces even lower than the ones indicated, but it is not always easy to secure them. The manufac- turers have been under such continuous and general pressure for high powers, and an uninstructed public has been so prone to test every telescope by its mere ability to carry high magnifications, that the makers have not been wholly to blame. But powers for each in- strument as low as the lowest prescribed above may usually be obtained, and are fairly satisfac- tory. The optical limit of lowest power is, of course, fixed by the light-receiving capacity of the eye. The diameter of the average pupil being \ of an inch, as we have seen, we must employ a magnify- ing power of at least 5 for every inch of aperture. The low-limit of power for a 3-inch telescope would therefore be 15 X. This is the theoretic limit. Practi- cally, however, there are few eyes that can well utilize so large an amount of light. There is also a high-power limit. Astronomers have frequently placed this at 100 for every inch of aperture. Upon this basis an eyepiece magnifying 300 times may be used on a 3-inch telescope and a power of 200 on a 2-inch. Formal tables showing, upon this basis, the double stars that different telescopes will divide have actually been published in reputable books. Nothing could be more misleading, especially to the beginner. "Indeed" says Newcomb, "it is doubtful if any real advantage is gained beyond 60 to the inch."* As the context shows, Newcomb has special reference to a large telescope, 24 inches in aperture, and, as he hastens to declare, his "remarks apply to the most perfect telescopes used under the most favor- able circumstances." He then proceeds, in terms too technical for quotation here, to describe some of the inevitable limitations of the telescope. We will deal below, in showing the advantages of low powers, with some of the simpler of these difficulties. It should also be said that the beginner does not have, with the astronomer, the advantages of training, — the trained eye and mind and hand. In the light, there- fore, of these considerations it should be clear that the average amateur observer, * Popular Astronomy, by Simon Newcomb, LL.D.; New York, American Book Co., p. 144. TELESCOPE— MODEL B All-Azimuth Mounling io6 a Beginner's Star^Booft especially at the beginning, cannot use to advantage a power of over 35 or 40 for every inch of aperture. This is the maximum, from the standpoint of practical experience. And in most cases the beginner will do well, especially at first, to work with eyepieces giving powers still lower. He will not thus see less than with higher powers ; he will actually see more, and what he does see will be seen with greater clearness and with far greater ease and pleasure. As he gains in experience he can begin the use of eyepieces of higher power. The Telescope Mounting The telescope tube is supported by a stand or tripod. Sometimes the instrument is merely provided with a stand of the "pillar and claw" type as shown in our illustration called Model A. This form of support is intended for use upon a table or upon a broad window sill. For packing or storing with the telescope, it has decided advantages but it is not usually a satisfactory model for serious work. Many of its disadvantages, however, can be overcome by careful managing. If it be used upon a table, see that the table rests sohdly and squarely on the ground or floor so that every possible source of unsteadiness may be provided against. Telescopes of this general type may be had of a number of makers and dealers, in sizes ranging from a "2-inch" to a "3-inch." The telescope marked here as Model B represents a more efficient type of tripod and is not much more expensive than the preceding. By far the greatest number of small portable instruments are mounted in this way. Each manufacturer varies the type a little, some making the tripods lighter or heavier than others, and securing the two motions necessary — a cross motion and a motion up and down — by different mechanisms. But all such mountings, from whatever maker, are extremely simple in design, are quickly under- stood and easily handled. While Model C represents the same general principle, it is heavier, its structure is more stable, and it possesses a more elaborate mechanism for increasing or decreasing the height of the telescope. The instrument here shown is pro- vided with a "finder," — a miniature telescope at the eyepiece end of the tube for aiding the observer in bringing objects into the field of view; § 13, p. 112. Tripods of this type are less portable than Models A and B but possess greater rigidity and steadiness. The models thus far mentioned. A, B, and C, represent, in principle, what is called an "alt-azimuth" mounting, a mounting permitting a motion in altitude and a motion "in azimuth" (or a motion up and down and right to left). The two motions permit the direction of the telescope to any point within convenient range of the observer. In Model D, however, we find the two motions necessary to the telescope secured in a some- what different way. This represents what is known as an "equatorial" mounting. Here, when the instrument is properly placed and adjusted, the fundamental axis is fixed parallel with the axis of the earth, running north to south. Free movements on the other axes of the instrument now give to the telescope the two motions provided by the preceding models. Assuming, for example, that the large end of our instrument points south, an observer stationed at the eyepiece will be able, when a star to southward has been brought into the field of view, to follow it in its course with only one motion of the telescope, the motion from east to west. This work can also be performed by an ad- ditional attachment called a "slow motion"; note the rod extending outward between the tripod and the eyepiece. And even this function is discharged, in instruments still more elaborate, by a "driving-clock" which, moving the tube in correspondence with the diurnal motion of the earth, enables the observer without effort to follow the course of the object in the sky. The "equatorial" mounting, with or without a driving-clock, is often pro- ■flnstruments of ©bservatlon 107 vided with "hour circles." Such an equipment ensures the accurate direction of the telescope to any object in the heavens, whether or not it may be seen by the unaided eye, provided its Right Ascension and Declination (the astronomical equivalents of longitude and latitude) are known. By a system of graduated circles adjusted to the axes of the telescope the instrument may be directed first to the proper Declination of the object, and clamped; it may then be turned to the object's Right Ascension (in hours, minutes, etc., — see note 14, p. 32). The star will thus be brought within, or very nearly within, the field of view. In- deed it should now be precisely in the field of the telescope if all the conditions of the case are accurately met. As most of the readers of this book will not possess instru- ments with hour circles I merely refer those who wish to make further study of their use to the volumes listed in the footnote.* To meet, however, the needs of instru- ments so equipped the places of the objects listed in the Observer's Catalogue of the present volume are indicated by Right Ascension and Declination, as well as by constellations. Such references are also of value to those who may use the charts of the celestial sphere at the close of the book, or who may desire to make use of celestial globes or larger star maps. In the location of the objects of observation, even when the telescope is without hour circles and not equatorially mounted, such refer- ences become increasingly helpful. Which of these various types of mounting shall the beginner purchase? The answer — for all cases — ^is not easily given. Each type has its strong points. Model D, if fitted with hour circles, should have the preference for advanced students, even though the instrument be without a driving-clock. But, in order to possess any real advantage over the simpler mounting represented in Models B or C, it must be accurately adjusted for latitude; it is heavier, more complicated, and not so easily managed. For the beginner, therefore, I do not hesitate to recommend the general form shown in Models B and C. These are purely illustrative. Both types of mounting are made by many different manufacturers in a number of designs; all representing the same principle of construction. The alt-azimuth type is less expensive as well as less complicated than the equatorial, and it is adapted, if well made, to all the ordinary needs of the amateur. *See Chainbers' Handbook of Astronomy, vol. i., the Oxford Press, 4th Edition, New York and London; Gibson's Amateur Observer's Handbook, Longmans, Green & Co., New York and London, p. 36 foL; Todd's New Astronomy, New York, American Book Co., p. 53. TELESCOPE — MODEL C Alt-Azimuth Mounting io8 a Beginner's Star^Booft The Telescope for the School In teaching the circles of the celestial sphere and in illustrating the theory of the science, the instructor may desire an "equatorial" mounting, but in the practical work of observa- tion, in introducing others — by simple object-lessons — to the pleasure and practice of viewing the things of the sky, the less elaborate mounting will meet the requirements even of the teacher. For high-schools and colleges I would strongly advise, where finan- cially possible, a telescopic equipment of three or four small instruments, rather than one very large one more elaborately mounted. Of this group of telescopes, the largest may have an aperture of 3 M or 4 inches and be mounted equatorially (if desired) ; the others may be of 3 inches in aperture (or even smaller) and on alt-azimuth mountings. Such an equipment, while not meeting an ambitious desire for an "observatory," will do far more than a great observatory instrument for the actual needs of the students. These, at least in earlier years, can hardly expect to become astronomers in the technical sense, but they should be permitted to share the interests and enthusiasms that follow from the direct personal observation of the familiar celestial objects. A little experience of this kind will often awaken ambitions for higher and broader work ; and it has its illustrative value for teachers as well as scholars. An equipment of small instruments has the following advantages over a single large expensive telescope : (i) It is possible in many cases in which the large telescope with elaborate mounting is impossible ; many a small institution which has no local provision for the large telescope can provide for the storage and keeping of a number of smaller ones. (2) This equipment will permit the simultaneous instruction, within a short period of time, of a larger number of observers. (3) With it, the really interested teacher can more quickly train adequate assistants from volunteers among the older pupils or from among associate teachers — if assistants should be. necessary. (4) The equipment of smaller instruments may be quickly unpacked and adjusted for use by one or two of the older pupils, — or even by an intelligent janitor, if need be. When work is completed the telescopes may be as quickly repacked, and stored. (5) The suggested equipment is far less expensive than a single large telescope on a stationary stand with an elaborate mounting. (6) Such a provision, even in institutions where there are large telescopes for observa- tory work, will free these larger instruments for their proper service under the observatory staff, and yet provide for the legitimate desire on the part of the students and others to see for themselves the objects of astronomical interest. Nearly all the characteristic objects of observation, see p. 3, can be seen by the beginner with far greater satisfaction in a small telescope than is commonly supposed. (7) The experience acquired will be all the more useful because gained from practise with such instruments as the average student may some day hope to possess. (8) The problem of bringing the telescope into the work or the recreation of the average school often resolves itself into the practical problem of finding the teacher who can under- take it. The plan suggested — a small group of several smaller instruments simply mounted — requires no special training. Such an equipment can be readily utiHzed. First Observations — The Advantage of Low Powers The telescope is usually dehvered to the purchaser in a box; the tripod being packed separately. In unpacking the metal parts from the box, note how the pieces He, in order llnstruments of ©bservation 109 that they may be easily replaced when you desire to return the instrument to the case. Fixmg the tripod in the open air for your first observations, see that its feet are evenly spread and that it is truly centred. All that contributes to its steadiness will help you to see ; all that interferes with its stability will make good seeing difficult. Whatever the form of the mounting, it should be strong and secure. A good, rigid support for the instrument is of fundamental importance. Almost the first question to arise will be, "What shall we look at?" Choose at first something quite easy. Let it be at night, if possible; the Sun is a poor first object. If the moon is in the sky, turn first to that. If the time be a winter's evening and Orion be in the sky, try an easy double star, — Delta (6), the top star of the Hunter's belt. See the Key- Map, p. 41 or 45. The star Zeta (C) in the Great Dipper, see any northward Key-Map, is also a fine first object. If the season be the late spring or early summer, try the star marked Beta (/3) in Scorpius; pp. 53 and 57. If one of the planets (Jupiter or Saturn) be well placed for observation, these are also superb first objects; see pp. 88 and 91. Mars and Venus are not so "consistently" easy. After removing the brass cap from the large end of the instrument, try to get a clear focus on the object, using the astronomical eyepiece of lowest power, — the eyepiece with the largest aperture, and with the largest ex- posure of glass on its interior surface. As you look through the telescope trying to find and view your first objects, you will perhaps be more or less baffled by certain troublesome impressions. The statement of these will illustrate the reasons for the repeated warn- ings to the beginner against high magnifying powers. If it were optically possible for the telescope to magnify the object alone, and to preserve it as a large image in a large well-lighted field, then we should want our magnifying power high, indeed the very highest. But this is not possible. Optically, there are some things as impossible to a telescope as for a good watch to tick seventy seconds to the minute. In magnifying the object, the very power used reduces the field of view in which it lies, the amount of light which illuminates this field, and magnifies not the object alone but every factor which involves or affects it as an image. The impressions to which I have referred are, therefore: 1. The impression that the world into which you are peering is dark, gloomy, and tractless. This impression is the more intensified, the higher the power you employ. 2. The impression, after you begin to see your way through your telescope, that the TELESCOPE— MODEL D Equatorial Mounting no H Beglnner'0 5tar:s»ooft circles or areas covered by your instrument are pitifully small. The smallness of the field you command makes it hard to find the object you are seeking. The field becomes smaller and this task of finding things becomes harder with the increase of magnification. 3. The impression that an object once found is wilfully determined to flit from the field of view as soon as sighted. This is partly due to the unsteadiness of your hand. Just as a power of 100 X will magnify the object, it will also magnify by 100 times, every touch or vibration of the hand, every disturbance caused by the wind or by heavy walking near the tripod. The lower the power, the smaller these exaggerations of motion. 4. The impression, even when the hand is removed and all is still, that the object is resolved to race away. There is now no touch of the hand, no unsteadiness, no vibration, — and yet "the thing will not stay!" There is one motion, however, that we may have forgotten. We know that all the objects of the sky, however stable they may be, seem to be slowly carried from east to west. This is due to the revolution of the earth on its axis. This rate of motion does not seem, superficially, very rapid; but multiply it by 100, or by 200, or by 300. When this apparent motion of the stars or moon or sun is thus magnified, we can readily see how quickly such objects must move across that little circle of sky which we have caught within our telescope. 5. The impression that as we attempt to follow an object in the field of view and to keep it near the centre, the object is deliberately "contrary," shifting to right or left in a direction precisely the reverse of the intention of the hand. This is based upon fact; all directions are reversed in the field of an astronomical telescope. The fact cannot be altered ; but the larger the field the less likely we are to lose the object by small false direc- tions of the hand. Low powers give this large field and permit an easier mental adjustment to the conditions. These impressions cannot all be removed at once by the use of eyepieces of low power, but they can be corrected. Thus the beginner can begin without a sense of despair and with somewhat of a sense of conquest. This sense of conquest will rapidly increase; and, as it increases, he will find increasing pleasure in his instrument. He will also find that he can, with more experience, use higher powers with advantage — changing his eyepieces and adapting the magnification of the telescope to different objects and to varying conditions. Some Practical Notes. 1. A dark-colored cap will sometimes be found attached to the astronomical eye- piece. This is for use only in viewing the Sun. It should be unscrewed and removed from the eyepiece in viewing other objects. See also p. 64. 2. Almost all observers work better while seated. Use an ordinary straight-back chair. Take the time and the necessary care to place yourself in a comfortable position. Strained postures and inconvenient attitudes are directly embarrassing to clear vision. 3. Be deHberate. Try not to hurry from object to object. Look with the mind as well as with the eye; this will help the eye as well as the mind. Try to refiect quietly upon the object under observation, returning to it repeatedly and noting any special peculiarities that may suggest themselves. 4. Street lights are sometimes a sore trial, especially when seeking to view objects near the horizon. A small sheet of cardboard slipped over the eyepiece end of the tele- scope will often prove a protection from their interference. Access to a good roof is an even better means of escape from such annoyances. 5. Work from smaller tasks to greater. The beginner may keep himself in a state of Unstruments of ©bservation III nervous discontent by a ceaseless expenditure of energy in the pursuit of objects just at the Hmit of visibiUty. Or he may take a wiser course, and prepare for these tests of vision by first learning to appreciate the many interesting objects within the normal capacity of his eye and his instrument. 6. In winter it is advisable to be warmly wrapped — for the physical exercise which so often protects us from exposure is missing while we are seated at the telescope. There are many observers who do not scorn the use of a hot brick as a foot-warmer. This if well-wrapped will keep warm for some time; and, when its heat is gone, another may be substituted. 7. To the beginner, the finding of objects with the telescope will at first seem difficult. If the eyepiece of lowest power is used, this will afford a wide and well lighted field of view and the object can be located more easily: a higher power, if desired, may then be sub= stituted without "losing" the object. A slight re-focusing will be necessary. As experi- ence increases, the finding of the desired objects becomes less difficult and is quickly accomplished. 8. It is usually best to meet the problem of "thick" weather by retreat, — unless you have much time to waste and much good temper to employ. As the telescope magnifies mist and fog as well as the objects of interest, it is at its worst under such conditions. If one will persist in working, and the mist be not excessive, the best objects under such con- ditions are the moon and the brighter planets, particularly Saturn — if these be in the sky. Whatever the atmospheric conditions, it is well — before beginning observations — to make a brief list of the objects to be noted. This will serve as a working memorandum and will usually save time. Begin with "easy" objects; not attempting things more difficult till the eye has been accustomed to the darkness. 9. Cleaning the lenses of an instrument is sometimes necessary. But it is best to use your lenses so carefully — ^protecting them from dust etc. — that this necessity may be rare. They bear a high polish. This may be seriously damaged by injudicious wiping and rub- bing. Scratches are far worse than a little dust. If dust accumulates remove it gently with a very soft camel's-hair brush, such a brush as may be bought for five cents at any druggist's. Special paper for cleaning lenses is often found at the optician's. If of the very best quality it may be tried, but much of it is worse than useless. The lenses may sometimes be dusted off gently with an old soft cambric handkerchief. The objective may be unscrewed from the tube, if absolutely necessary, but the two lenses of which it is composed should never be taken apart except by the manufacturer. ID. The habit of pointing a telescope from the window of a room is not to be com- mended. Still less should a telescope be pointed through a pane of glass, however clear. Distortion must result. The instrument should be taken into the "open," even if one can do no better than place it on a veranda. If this be impossible and a window must be used, all light in the room should be turned out, and time should be given for the pupil of the eye to grow accustomed to the dark. In the dark the pupil grows larger and the eye keener. The temperature in the room should also be permitted — if possible — to approxi- mate the temperature outdoors, if the telescope is to do its best work. The larger the instrument, the more need there is to let the air in the tube come to the temperature of the air outside, that the images seen in the telescope may be steady and clear. II. For this reason it is well to permit the telescope to "cool off" for a few minutes, if taken from a warm room in winter and set up outside. Time should also be given to the pupil of the eye to dilate in the duller Hght of the out-of-doors. Good work cannot be done with an eye contracted by the illumination of a brilHantly lighted room, peering 112 a BeGlnner'0 Star*36ooft through a telescope in which the hot air is in process of "boiling-down" to the temperature of the outer cold. Sir John Herschel, before attempting to verify his father's observations on the satellites of Uranus, kept his eyes in total darkness for fifteen minutes. Such extreme precautions are not necessary with small instruments; but the general suggestion is important. 12. The beginner will sometimes feel the telescope to be a strain upon the eyes. Closing one eye while looking through the instrument with the other eye is at first a weari- ness to both. This weariness often wrongly suggests that something is the matter with the eyes. These difficulties, however, are almost entirely muscular. The proper muscles soon become used to the new way of seeing; and the observer soon finds that he can use his instrument for long periods with no sense of strain or discomfort. Near-sighted observ- ers need not retain their glasses; the instrument, with proper focusing, will correct the difficulty : the eyepiece should be pushed a little farther into the tube. Even with normal eyes the one used most actively may be soon wearied. If so, it may be given brief intervals of rest, and the need for these will decrease as experience grows. A few observers find that an eye-cap of dark cloth over the unused eye is an advantage. One needs to avoid the undue exhaustion of the nervous and muscular forces of the eye, but this danger is no greater at the telescope than at any other interesting work. In many cases the vision is stimulated, trained, and positively improved. 13. The optical equipment of a telescope usually includes at least one terrestrial and two or more astronomical eyepieces. If the terrestrial eyepiece is omitted, the purchaser may fairly ask a larger astronomical equipment ; for its money value — compared with the latter — is about as 2 to i. Extra attachments, usually at additional expense, may be had, — such as a diagonal eyepiece for viewing objects too near the zenith for convenient observation, and a "Herschel" eyepiece for reducing the light and heat of the Sun to the eye. The latter is discussed in the chapter on the Sun. The diagonal eyepiece makes the finding of objects more difficult, and it deprives the observer of the sense of direct vision. Many find such an attachment of great convenience, however, in viewing objects that are too high up for comfortable study with the ordinary equipment. The attachment is "popular," though its cost is high in proportion to its actual working value. The diagonal eyepiece is shown on Model D, but it may also be obtained with practically all telescopes over two inches in aperture. On Model D and also on Model C is shown a "finder," a miniature telescope placed near the eye-end of the larger instrument. With its low-power eyepiece it affords a very large field of view. This is divided by two cross wires which by their intersection mark the centre of the field. The finder is so adjusted that when an object is brought to the centre of the field of view in the finder, it will be found at the centre of the field in the telescope proper, the two centres being coincident. This attachment is extremely desirable on instruments over three inches in aperture. Tele- scopes of three inches and under do not need it. In the finding of objects, as has been already suggested, a low-power eyepiece may be used on the telescope itself, and, when the object is found, a higher power — if desired — may be substituted. 14. First impressions are sometimes disappointing. The distance of the stars is so great, see p. 9, that the facts transcend all our ordinary standards of comparison. Whea. we are told in one sentence that a celestial object is at least 1000 times larger than our Sun, it seems wholly absurd to learn in the next sentence that though we may use upon it a magnifying power of 100 diameters the telescope can show it to us only as a brilliant point of light. Let us suppose, however, that we were able to use a telescope magni- fying not 100 but 10,000 diameters. As such a telescope — even if its construction were ■flnstruments of ©bservatlon 113 possible — would magnify all the conditions of atmospheric obscurity or disturbance (as well as the star) no one could use it. But on the assumption that we could use it, what would it do for us? It would bring a star that might be lo million million miles from us to an apparent distance of looo million miles. That is not very near! But there is no star so near as lO million million miles. The very nearest is 4.3 light-years, or 25,000,000 milHons of miles away; and no star so near as that can be seen from the latitudes of Europe or North America. Most of the stars are at far greater distances. As we bear these facts in mind, we need not be surprised if the telescope does not make any of the fixed stars assume the proportions of a tea-cup. In the case of the objects of our solar system — the Sun, the moon, the planets — an apparent enlargement of the image may be had. But there are many who find disappointment even here. Says Webb: "In viewing Jupiter in opposition with a power of 100, they will not believe that he appears between two and three times as large as the moon to the naked eye; yet such is demonstrably the case. There may be various causes for this illusion ; — want of practice, of sky-room, so to speak, of a standard of comparison. A similar disappointment is frequently felt in the first impression of very large buildings; St. Peter's at Rome is a well-known instance. If an obstinate doubt remains, it may be dissipated forever when a large planet is near enough to the moon to admit of both being viewed at once — the planet through the telescope, the moon with the naked eye."* 15. A telescope equatorially mounted, having hour-circles but with no sidereal clock, may be directed to an object invisible to the naked eye by the following method. Note and record the difference in Right Ascension between the required object and some known object that may be readily recognized. (The beginner should remember, in calculating the difference in R. A. between two objects, that if this difference is greater than 12 hours the number 24 must here be added to the smaller R. A. before subtracting.) We proceed on the assumption that the object sought is toward the south. If the R. A. of the object sought be greater than that of the known object the former will be farther east ; if the R. A. of the object sought be smaller, that object will be the farther west. Using your eye- piece of lowest power, direct the telescope to the known object, bring it to centre of field, and read the hour-circle. Now move it east or west, as need may reqmre, until the index of the hour-circle has moved through a distance equivalent to the difference in the Right Ascensions. Now set the Declination circle, and the required object will be found within the field. Gibson wisely suggests that the known object be selected, if possible, on the same side of the meridian as the object sought. 16. Telescopes variously mounted and fitted with adequate eyepieces may be had in the United States at the following retail prices. These prices are not to be taken as from the catalogue of any particular manufacturer. They are to be regarded as rough approximations, here introduced merely as a general guide to the purchaser. Telescopes of from 2 inches to 2 3^ inches in aperture may be had at from $60 to $85, according to quality and type of mounting. There is usually not much difference in cost between a 2-inch and a 23^-inch, and — other things being equal — the 23^-inch is, of course, to be preferred. The same consideration applies to telescopes of 23^ to 2^4 inches in aperture. These may be had at from $65 to $120, according to quality and type of mounting. The simple mountings cost less, and are usually efficient enough to meet the needs of the average observer. * Celestial Objects for Common Telescopes, T. W. Webb, M.A., F.R.A.S., vol. i., p. 16, ed. of 1907; Longmans, Green & Co., New York and London. 114 H Beginner's StaivBooft Telescopes of 3 inches in aperture fitted with one terrestrial and at least two astro- nomical eyepieces can be had at from $75 to $170. Here again the simple "alt-azimuth" mounting is quite adequate for all ordinary purposes. The prices of telescopes over 3 inches in aperture I do not attempt even to suggest — the variety is so great and the range of values is so large. If one desires, one can put as much as a thousand dollars into a 5-:nch portable telescope. There are also instruments on the market at prices lower than any here quoted. With- out judging them, I have preferred to speak only of -values that are personally known to me. Teachers and all who are on the purchasing committees of schools and colleges will take satisfaction in learning that the high customs tariff on telescopes of foreign manufac- ture is not applicable to instruments purchased for the use of educational institutions. Deductions, therefore, from the prices above quoted — ranging from 20 to 35 per cent. — are not infrequently made. The transaction, however, must represent a direct importa- tion, must be in the name, and for the use of, the institution, and instruments thus imported must not be for sale. 17. A few final notes are here thrown together. — In using the Key-Maps for the telescope, the beginner should first read the accompanying notes under the Night-Chart on the pages opposite. — Always remember, in using any of the Key-Maps, to begin as near as may be feasible at the centre of the map, working from the centre outward. — While the telescopic objects are classified roughly for (I) the Opera-Glass and the Field- Glass, (II) the Two-inch Telescope, and (III) the Three-inch Telescope, these divisions are necessarily somewhat arbitrary. An object listed for a 2-inch, may be seen to even better advantage in a 2}^, or 23^, or 2^, or 3-inch; and some of the objects classified for the 3-inch may be well observed, under good atmospheric conditions, through smaller telescopes, — especially if the observer has had the advantage of a little experience. Those, moreover, who possess 4-inch or even 6-inch telescopes will find that the selected objects are not less interesting or less beautiful because adapted to smaller apertures,^ any more than a drop of water is less interesting as we increase the range or refinement of the microscope. Should the observer wish to work in entire independence of the classi- fications under the Key-Maps, he has only to turn, in the Observer's Catalogue, to the constellation desired, where the best maps are indicated and all the important objects noted. — The beginner is reminded that in viewing the full moon there are certain advan- tages in using the terrestrial rather than the astronomical eyepiece; the additional or erecting lenses serve to reduce the excessive brilliancy of the object. See pp. 70, 71.^ Teachers who may wish information as to the adaptation of this book to their educa- tional work (either alone or for supplementary use) may obtain a special circular on application to the author, in care of the publishers. " Herbert Spencer has somewhere reminded us that the crowbar is but an extra lever added to the levers of which the arm is already composed, and the telescope but adds a new set of lenses to those which already exist in the eye. In a very deep sense all human science is but the increment of the power of the eye, and all human art is the increment of the power of the hand. Vision and manipulation, — these, in their countless indirect and transfigured forms, are the two cooperating factors in all intellectual progress.'' — John Fiske; The Destiny of Man; Chapter VII NEBULA IN SAGITTARIUS, KNOWN AS MESSIER 8 From a photograph taken at the Yerkes Observatory 115 IDim. a Brief ©bserver's Catalogue of telescopic ©bjccts This Catalogue is limited to objects of the Stellar World; for the objects of the Solar System, see Chapter V. Explanatory. The objects discussed under the Night-Charts and Key-Maps, pp. 38 to 61, are there given reference numbers in brackets [ ]. These refer to corresponding numbers in this catalogue. The catalogue will thus be found to contain a good deal of material for which there was not space under the maps. Some of this the beginner may not at first want, but there will be an increasing desire for additional facts as interest and knowledge grow. Here are given, also, the positions of the stars by l^ight Ascension and Declination — for the use of those who may possess instruments with hour-circles (see p. 107) and for all who may desire to find the places of the stars, in star atlases or in charts of the celestial sphere, with more precision than is possible in a mere general reference to the constellation. See note 14 on page 32. While the telescopic objects are chiefly noted under the Key-Maps on the right-hand pages, 39 to 61, the beginner should not fail to read also, in each case, the matter under the corre- sponding Night-Chart. A few telescopic ob- jects not noted under theKey-Maps are included in this Catalogue. Here also will be found indicated the exact magnitudes of the stars. These are given according to the Revised Harvard Photometry, 1908. In some cases the magnitudes of the smaller components of the double stars are not given in that list. In such instances they are chiefly taken from the Sternverzeichniss of Ambronn, Gottingen, 1907, as stated in the preface to this book. From that compilation I have also taken the estimates of star colors, and where these are omitted in the Ambronn list, I have fallen back on the impressions of Webb or Smyth, except where very subtle distinctions of color have seemed overdrawn. Small instruments do not show, as a rule, any but the clearer and sharper color-contrasts; but much depends, of course, upon the quality and construction of the telescope and on the local conditions of light and air. More still depends on the personal equation of the obser- ver, — some eyes are color-blind; some, if the term may be coined, a,re color-wild, seeing hues and tints "that never were on sea or land." Avoiding both extremes, the beginner will find much of charm and pleasure in the study of color-contrasts. Here also are given the distances between the components of double or multiple stars, as measured in seconds of arc. Thus the observer may secure a general idea as to the distance at which he may expect to find the members of a composite system. A still greater help in detecting faint companion stars may be obtained from a rough knowledge of "the position angle." The beginner will do well, at the very first, to confine his obser- vation to double stars in which the compo- nents are rather widely placed and so bright as to make a knowledge of the position angle unnecessary. To some minds the understand- ing of position angle measures is very easy; to others it is difficult. The chief point to be remembered is that the amateur may find much pleasure in the observation of such stars without going into the question at all. As the observer comes to take up the subject, a few words of explanation may be useful. POSITION ANGLE OF DOUBLE STAR As shown in Astronomical Telescope, linage Inverted The angle is reckoned from north {below) at zero; through east (po ) ; and south, l8o°; round through 270°, west; to completion of circle at 360° First, let us assume that the angle is measured when the star, as we face south, is on the me- ridian; — that is, at the moment when the star culminates or reaches its highest point in its course from east to west. Let us thus first secure our mental picture of the position angle as an angle measured not at the moment when the star rises or sets or is east or west, but at its upper culmination. 116 Hn Observer's Catalogue 117 Of the two lines, therefore, which meet at a point and form the position angle, one is the line from north to south running through the brighter _ component of the culminating star (as the line o to i8o in this diagram), the other line is that connecting the two components of the star, A to B. This line is always drawn in imagination from the brighter to the fainter component; and the angle is reckoned, as in the field of an astronomical telescope, from below at zero around to B. In our illustration, for example, the position angle of the double star A-B is 210 degrees. We learn in this way the direction in which to look for the fainter component of a double star. Delta (^) in Corvus, for example, has almost the same position angle as that shown in our diagram. In the sketch given on page 26, Delta ((5) is the brighter of the two stars at the upper left-hand corner. The smaller star there shown should not be confused with the telescopic companion. When Corvus is due south or approximately south, see position B, page 26, the small component will be found upward and to the left, — about as in our dia- gram here. As Delta (d) rises — or when the constellation, p. 26, is at position A — the posi- tion angle is of course unchanged but the appar- ent direction which it indicates will vary with the position of the group. At A, therefore, the telescopic companion will appear lower down and toward the left. As the star swings westward to position C, page 26, the small companion will appear upward and to the right. Turn now to page 25, and note the case of Delta ((5) in Orion, the uppermost of the three stars running diagonally through the square. The position angle of this star is 0°. It might also be written 360°, as we may see from our diagram, p. 116. This means, of course, that when Orion is at position B, due south, the fainter component is directly below the brighter. We may see, however, from the illus- tration on page 25, that when Orion is east- ward, at position A, the small companion to Delta (<5) must appear below, but to the right; and that when Orion is at position C, it must appear below and to the left. For the appar- ent direction of the companion will naturally change, as in the case already cited, with the changing "slant" or inclination of the group. This will become quite clear with a little actual experience in observation. In studying our diagram of a position angle, the reader should note that it is drawn for use as the observer faces south. In facing north- ward the beginner should remember that since the zero-point must always be toward the north pole, the top and bottom of the diagram will be reversed for stars culminating between the pole and the zenith. For the northward stars when below the pole, the diagram requires no inversion. References will sometimes be found in this catalogue to double-stars as "doubles," to a star with three components as a "triple," etc. In many cases a double-star is known to repre- sent a system in which both the components are in revolution about a common centre of gravity. Such doubles are called "Binaries " All binaries are double, but all doubles are not necessarily binaries. References will also be found to "spectroscopic" binaries. These are binary systems in which the components are so near that their division or separation can be detected- only by the spectroscope — being too close together for the telescope to show them as separate objects. A full discussion of the spectroscope and of its marvellous revelations lies outside the plan of this book; the reader may find such information in some of the volumes noted on page 144. Here it may only be crudely said that these results are obtained in the case of each star by the study of the composition and action of its light. Investigations also conducted with the spectroscope have told us that the stars have besides their "apparent" motions (such, for example, as the motion from east to west caused by the revolution of the earth) and their " proper motions" in space, see pa,ge 139, definite individual motions in the line of sight, motions directly toward, or directly away from, our solar system. When the reader finds, therefore, in this catalogue that a par- ticular star is said to be approaching the earth or receding from the earth at the rate of 10 or 15 miles a second, it should be understood that the instrument which brings us such results is not the telescope but the spectroscope. The facts as to the actual movements of the stars are so striking that they might awaken our alarm but for the consideration that the stars are almost inconceivably far away, so far indeed that these movements may possess for us an element of interest but not the least element of anxiety. The same consideration should be borne in mind in thinking of the "proper motions" of the stars; p. 138. For the stars are not really at rest. They seem so to be, because of their great distance from us. But most of them, like the Sun itself — our own star, — are moving through space at high velocities. References, therefore, will also be given here to the distance from us of certain of the stars, and a table dealing more fully with the data will be found on page 139. The instrument by which the most trustworthy of these results have thus far been obtained is a modification of the telescope called the heliometer. Other methods, some of them employing photo- graphy, for the determination of star distances are now being matured. Ii8 H BeGinner'6 Star*Booft The first association of the stars into con- stellations or star-groups is prehistoric. Some of the most familiar — such as Orion, the Pleiades, the Hyades, as well as the stars Sirius and Arcturus — were known to Hesiod (c. 800 B.C.) and they appear in Hesiod as already well known and long established. The earliest formal lists are those of Eudoxus and Aratus (c. 400 and c. 270 b. c.) though it is to Ptolemy (150 A. d.) that we owe the full list of 48 constellations familiar to the ancient world. Of these, the niost important are those of the Zodiac; see p. 80; namely, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aqua- rius, and Pisces. Those north of the Zodiac in Ptolemy's list were: Ursa Major, Ursa Minor, Draco, Cepheus, Bootes, Corona Bo- realis, Hercules, Lyra, Cygnus, Cassiopeia, Perseus, Auriga, Ophiuchus, Serpens, Sagitta, Aquila, Delpliinus, Equuleus, Pegasus, An- dromeda, Triangulum ; and south of the Zodiac as follows: Cetus, Orion, Eridanus, Lepus, Canis Major, Canis Minor, Argo, Hydra, Crater, Corvus, Centaurus, Lupus, Ara, Corona Austrina, and Piscis Austrinus. The myths or legends connected with the more important of these are given in this Observer's Cata- logue in their Greek forms, — though the Greek version is often but the recasting of an earlier myth. Abbreviations. The ob j ects listed are grouped by their constellations, in alphabetical order. First, comes the name of the constellation. Then follow page references to the Key- Maps in which it is to be found for observation in the evening sky. Then come references to N. H. or S. H. (northern hemisphere or southern hemisphere), indicating the mean Right Ascen- sion (R. A.) and Declination (D.) of the group, for reference to the hemispherical maps at the close of the volume. As the map of the north- ern hemisphere contains a large overlap of the southern sky, the abbreviation N. H. at this point does not necessarily mean that the object is north of the equator but merely that reference is made to the first (and larger) of the two maps. See note 14, p. 32. The celestial equator should not be confused with the ecliptic; it will be found to run through Hydra, Orion, Aquila, Serpens, etc. The letters S. H. refer to the map of the southern hemisphere, the smaller of the maps at the book's close. In writing of the double or multiple stars, the letters A, B, C, etc., usually refer to the components in order of brightness. The word "distance" is used for the distance between such components; and the letter p. for the position angle. The abbreviation Mag. refers to the magnitudes of the stars; — not their physical size or their actual luminosity, but their relative brightness as seen with the unaided eye or with the telescope. In the case of double stars, the position assigned (in R. A. and D.) is for the brighter component; and for the year 1900. Following recent usage, the fractional parts of a minute (in noting R. A.) are here expressed not in seconds but in decimals. One minute and thirty seconds, for example = 1.5 m. A'-cher-nar, see [175]. Al-deb'-a-ran, see [381]. Al-tair', see [21]. I. — An-drom'-e-da (Maps pp. 55, 43, 61, 41. N. H., R. A. I h., D.+40°). A fine constella- tion lying between Perseus and Pegasus, its brighter stars forming an almost straight line. According to the Greek myth, Andromeda was the beautifiil daughter of Cepheus, king of the ancient Ethiopia, and his queen, Cassiopeia. The queen in the pride of her own beauty sat one day enthroned by the sea, plaiting "ambrosial tresses." There, in the hearing of the sea-n3rmphs, she boasted that she was fairer than they. Deeply enraged they succeeded in having a sea-monster sent to ravage the coasts of the kingdom. Ap- pealing for help, Cepheus and his queen were informed that the penalty could be averted only by exposing their daughter, Andromeda, as a prey to the monster. She was chained to a great rock by the sea to appease him. There she was seen by Perseus, returning from his victory over the Gorgon. The head of Medusa, which turned all who beheld it to stone, he bore in his hand. Calling to An- dromeda and bidding her to avert her face lest she perish also, he turned the sea-monster into a huge rock. Then cleaving with his sword the chains which bound the wrists of the maid, he bore her away as his bride. At death they were placed with Cepheus and Cassiopeia among the stars. The story is finely told by Charles Kingsley in his Greek Heroes. A later legend finds in Cetus, the Whale [no], the Monster of this older myth; and in Pegasus, the Winged Horse [301], the steed on which Perseus bore Andromeda away. 2. — The famous nebula, M 3 1 , is not conspicuous in small instruments, but of great interest. R. A. o h. 37.2 m., D.+4o° 44'. An illustra- tion of the nebula will be found on p. 20. The estimate of its dimensions as given on p. 21 is based on an assumed parallax of o".oi (see Introd. to Astronomy, F. R. Motdton; New York; edition 1910, p. 541), and is prob- ably an understatement rather than an over- statement. The actual form of the nebula is probably less oval than shown in the engrav- ing. Some observers regard the oval shape an ©^server's Catalogue 119 as wholly due to the way in which the object is tilted to the line of sight, but that its form is strictly circular is highly doubtful. Its appearance in a small instrument is somewhat disappointing. The striking and beautiful impression given by the camera is due not only to the efficiency of the telescope em- ployed but to the long exposure of the photo- graphic plate. This is the largest of the spiral nebulae. The great nebula of Orion [294] is quite as large, if not larger, but irregular in form. 3. — Gamma {y) is a double star, one of the most beautiful of telescopic objects. It forms a right-angled triangle with the stars Beta (/J) and Alpha (a) of Perseus; or it may be found by running an imaginary line from Polaris to Epsilon (fi) in Cassiopeia and continuing it an equal distance. Mag. of components, 2.3 and 5 ; A orange, B emerald ; distance = 10" ; p. = 63°, R. A. Ih. 57.8 m.; D.-f4i° 51'. B is also a double in a large telescope. The Arabic name for Gamma (y) is Alamak. The star is ap- proaching the earth at the rate of 6.84 miles a second or 410 miles a minute. See Table, p. 139- 4. — Pi (tt), a double star, mag. of components, 4.5 and 9; A white, B blue; distance = 36" ; p. = 174°; R. A. oh. 31.5 m.; D.-|-33° 10'. It is interesting to note that this star is receding from the earth at the same rate of motion at which Gamma (y) is approaching, 6.84 miles a second; seee above. 5. — The little star marked j6 is an easy double ; mag. of components, 6 and 5.8; both yellow; distance =i8i".6; p. =301°; R. A. I h. 50.2 m.; D.+36° 46'. An'-ser, see Vulpecula [425]. Ant-a'-res, see [351]. An-ti'-no-us, see Aquila [20]. 1 0. — Ant '-lia, the Airpump . ( Map p . 49 . S . H . , R. A. X h.; D. — 30°.) An unimportant southern constellation, too low in the sky in our latitudes for satisfactory observation ; few objects of interest. 15. — A-qua'-ri-us, the Water-Bearer (Maps pp. 61,57,41. R.A. XXIIh.; D. — 10°). A large constellation, important because lying in the Zodiac or pathway of the planets, see p. 80, but it is not conspicuous, having no stars greater than the third magnitude. 16. — The globular cluster marked M 2 is not brilliant. Located by imaginary line from Zeta (C) in Capricornus to Beta (/3) in Aquarius, and slightly continued. R. A. XXI h. 28 m. ; D. — 1° 16'. 17.— The star Zeta (C), at the centre of the Y-shaped figure marking the mouth of the "water-jar," is a strikingly interesting double, the components being of almost the same mag- nitude. Mag. of components, 4.4 and 4.6 ; colors, both white; distance = 3"; p. = 317°; R- A. XXIIh. 23.7 m.; D. — o°32'. 18. — The star Psi (i/j') is an easy double even in a 2-inch instrument. Mag. of components, 4.5 and 8.5; A vellow, B blue; distance = 49" ; p. = 312°; R. A.'XXIIIh. 10.7 m.; D.— 9°38'. 20. — A'-quil-a, the Eagle (Maps pp. 57, 61, 53. N.H.,R. A.XIXh. 2om.;D.-f 5°). The stars of Antinoiis are now included in Aquila. As this constellation lies in the Milky Way, it presents rich fields for all low-power instru- ments, though containing few easy doubles. 21. — Altair; a fine first-magnitude star, forming with Beta (/3) and Gamma (y) one of the clear- est landmarks of the summer sky. R. A. XIX h. 45.9 m; D. -\- 8° 36'. I have called the linear figure formed by Alpha (a). Gamma (y), and Beta (/3) the "shaft of Altair." Altair, next to Sirius and Pro'cyon, is the nearest first mag. star visible from northern latitudes, being at a "light-distance" of 14 years; see p. 9. Altair's annual proper motion is quite sensible, being o".65. It is yellowish white in color; — of the same general type as Sirius. It is approaching the earth at a velocity of over 1200 miles a minute. 22. — Very near to Lambda (A.) is a small double, not charted but easily found ; marked as 75 in some maps; mag. of components, 5.5 and 7.5; A white, B lilac; distance = 34". 5; p.=2o6°.6; R. A. XVIII h. 59.7 m.; D. — 4° 11'. 23.— A rich cluster marked M 11 ; R. A. XVIII h. 45.8 m.; D. — 6°24'. Arc-tu'-rus, see [41]. 25. — Ar'go Na'-vis, the Ship Argo. A large constellation, most of which is too far south for satisfactory observation in our latitudes. Some stars of Puppis appear low down in Maps pp. 45, 49; but for the whole constella- tion see S. H., R. A. IX h.; D.-55°. Some- times divided into four parts — Puppis, the stern ; Vela, the sails; Carina, the keel; and Pyxis, the compass. 26. — The cluster marked M 46 is sometimes listed as 1564, or 2437. It is not difficiilt, forming an interesting object for small instru- ments. R. A. VII h. 37.2 m.; D. — 14° 35'. 27. — Can-o'-pus, the leading star of this con- stellation, the Alpha (a) of Argo (more specifi- cally of Carina) is second only to Sirius [66] in brilliancy, but as it is very much more remote, being at a distance of, at least, three hundred light-years, it is probably many thou- sands of times greater in mass. It is a star of the same type as Procyon; though enormously larger in size. It has an annual proper motion of o".02 and a motion of 12 miles a second away from our system. 120 H Beginner's Star^Book 30. — A'-ries, the Ram (Maps pp. 61, 41, 55, 45, 43. N. H., R. A. II h. 30 m.; D. + 13°). An important constellation, lying in the Zodiac or pathway of the planets; see p. 80. This con- stellation, as will be seen by reference to the N. H. map, covers a far wider area than the region marked out by its three most con- spicuous stars. According to one of the Greek mj'ths, the mother of Phrixus and Helle gave to the former a ram having golden fleece. Fleeing from Hera, their step-mother, they reached the sea ; and both attempting to cross on the ram's back, Helle was drowned (hence the Hellespont). Phrixus, after his escape, sacrificed the ram, and dedicated the fleece to Zeus. The fleece was carried away by Jason; but Zeus per- petuated the memory of the ram by giving it a place among the stars. 31. — Lambda (A), a fine double star, mag. of components, 5 and 8 ; A white, B blue; distance = 38"; P-=45°; R. A.I h. 52.4 m.; D.+23°;'. 32. — Gamma (y) — the Arabic name is Mesartim — is an easy double star. It was discovered by Hooke in 1664; though it was not the first double star discovered, as is sometimes stated; see [401]. Mag. 4.7 and 4.8; A white, B pale gray; distance = 8". 6 ; p. = 360°; R. A. I h. 48 m.; D.-|-i8°48'. 33. — ^The star jo is also a double. It bears no symbol in the Key-Maps, but it will be found just to one side of a line from Alpha (a) to Beta (/S), continued a little over twice that dis- tance. Mag. 6.6 and 7.4; A yellow, B gray; distance = 39"; p.=273°; R. A. II h. 31.2 m.; D.+24° 13'. 35. — Au-rl'-ga; the Charioteer. (Maps pp. 59, 47, 45, 41, 39. N. H., R. A. V h. 30 m.; D. -f- 42°.) This constellation, among the ancient Greeks, was connected with several myths. Among these may be mentioned the story that the group represents Erichthonius, sonof Athena and Hephsestus, who was thus given a place among the stars because of his invention of the chariot. The name of the constellation appears in the Greek star lists of Eudoxus (4th century B.C.) and Aratus (3d century B.C.). 36. — Ca-pel'la, the leading star of the constel- lation, is accompanied by three fainter stars forming to the eye a small acute triangle. These, Epsilon (f). Eta (77), Zeta (C), are called the Kids, Capella itself meaning, literally, the she-goat. The presence of "the kids" will always serve to distinguish Capella, in a clear sky, from the other bright stars. The group is situated so far to the northward that in its revolution about the Pole it is carried below the horizon, in our latitudes, for only a short period of time and so is almost always in our skies. Capella is brilliantly yellow or golden in color, and so much larger than our Sun that whereas Capella shines to us as a first magnitude star, the Sun at the same dis- tance would appear as a star of only the fifth or sixth magnitude. Capella is a spectro- scopic binary with a period of 104 days; see p. 117. It is at a light-distance of 49 years; and is receding from our system at a velocity of 18.6 miles a second. R. A. V h. 9.3 m. ; D. -1-45° 54'. Exact mag. 0.21. 38. — The small star marked 14 is an easy double, Mag. 5.1 and 7.2 ; A yellow, B blue; distance = I4".5; p. =225°. R. A. V h. 8.9 m.; D.-I-32'' 34' ; the star is triple in large instruments. Bet'-el-geuze, see [291]. 40. — Bo-o'-tes, the Herdsman. (Maps pp. 53, 49> 43. 47. 55. 57- N. H., R. A. XIV h. 30 m.; D. -|- 30°. A large and important constella- tion of the northern hemisphere, south of Ursa Major and west of Corona. The con- figuration of the Herdsman as it is usually suggested will be found in the text under the Night-Chart on p. 42. While not in the Zodiac, or pathway of the planets, Bootes is among the first recorded constellations. 41. — Arc-tu'-rus; a superb first-magnitude star, R. A. XIV h. ii.i m.; D.-1-I9° 42'. Next to Sirius, Vega, and Capella, Arcturus is the bright- est star visible from northern latitudes. Indeed it is rated in the Revised Harvard Photometry (1908) as of mag. 0.24, — nearly the same as Capella (0.21). The star is of a deep yellow color, possessing at times an almost reddish cast. Its motion in the line of sight (186.6 miles a minute) is toward us, but this ve- locity, as compared with many of the stars, is not high. The proper motion (see p. 138) of Arcturus is, however, unique amiong cur brighter stars, making it an object of sur- passing interest. This great star, at least 1000 times the size of our sun in volume, is rushing through space at a velocity of nearly 90 miles a second, or over 320,000 miles an hour. The direction, according to Newcomb, is southwest, or toward the constellation Virgo. We must remember, upon the other hand, that as Arcturus is so far distant from our system, light from the star requiring more than forty years in which to reach us, the high velocity of its motion has not altered its appar- ent position in the sky in 4000 years by much more than 2^°, or 5 times the apparent diameter of the moon. No change in its position within a century could be detected except by the use of instruments of high pre- cision. The advanced student should bear in mind that the above statement is based not on the parallax for the star of o".03 for some time current, but on the corrected paral- lax of o".075; see p. 139. 42. — Epsilon (f), a beautiful double star, but the- beginner will find it difficult even with a three-' inch instrument; mag. 5.1 and 2.7; A pale an ®b0erv>er's (EataloQue 121 orange, B green; distance = 2".7; p. =330°; R. A. XIV h. 40.6 m. ; D. +27" 30'. Arabic name, Izar. 43 -—Delta ((5), double star; mag. 3.6 and 8; A pale yellow, B light blue; distance = 105"; p. = 79°; R. A. XV h. 11.5 m.; D. + 33° 41'. 43b. — Xi (S), double star; mag. 4.8 and 6.6; A yellow, B purple; distance = 3"; p. =200°; R. A. XlVh. 46.8 m.; D. + i9°3i'. 44- — Pi (^). double star; mag. 4.9 and 5.8; colors, both white; distance = 7"; p. = 100°; R. A. XIV h. 36 m.; D. + i6°5i'. 45. — Kappa (k), mag. 4.6 and 6.6; A white, B bluish; distance = 13"; p. = 238°; R. A. XIV h. 9.9 m.; D. + 52° 15'; not far from Eta ('/) of the Great Dipper. 46. — Iota (z) mag. 5 and 7.5; A pale yellow, B white; distance = 38" ; p. = 33°; R. A. XIV h. 12.6 m.; D. + 5i° 50'. 47. — Mu (/^Oi mag. 4.5 and 6.7; both white; dis- tance =108"; p. = i7i°.6; R. A. XV h. 20.7 m.; D.+37° 44'. 48. — Cam-el-o-par'-dus, the Giraffe (Maps, all northern; N. H., R. A. V h.; D. + 70°). A large but dull and unimportant constella- tion near the Pole. 49. — The star marked ig H is an easy and pretty double. Mag. 5 and 8.5; A yellow, B blue; distance = i6"; p. = 10°; R. A. V h. 6.1 m.; D. + 79° 7'- 50. — Can'-cer, the Crab (Maps pp. 45, 49, 39, 51 . R. A. VIII h. 25 m.; D.+20°). A small dull constellation, but of importance because lying in the Zodiac or pathway of the planets. 52. — A fine cluster called Pras'-se-pe, or the Beehive. The stars of this famous cluster are not so numerous as in many other clusters, but of sufficient magnitude to make a beauti- ful object in ' a small instrument. Galileo counted 36 soon after the making of his first telescope; later observers have counted over 300. R. A. VIII h. 34.7 m.; D. +20°. 53. — Iota (0 is a fine double, small but not difl&cult; mag. 4.2 and 6.6; A faint orange, B blue; distance = 31"; p. = 307°;R. A. VIII h. 40.6 m.; D.+29° 8'. 54. — Zeta (y is a remarkable triple star; only 2 components can be easily seen in small telescopes; mag. 5.6, 6, and 6.3; A B yellow, C orange; distance (AB-C) =5"-5; P- = ii5 I R. A. VIII h. 6.5 m.; D. + i7° 57'- "One of the most remarkable multiple stars. The orbit of A and B has been well determined; they revolve about each other at a distance of less than i", in a period of 60 years, and a're accom- panied by a third star, C, which revolves about the centre of gravity of all, in an opposite direc- tion. From irregularities in the motion of C, it is concluded that it is a satellite of an in- visible body around which it revolves in 17I years, describing an ellipse with a radius of about 5 of a second, and that the two together circle around A and B in 600 or 700 years." — - Sir Robert Ball. 55. — The cluster marked M 67 is composed of stars of mag. 9-12.5, surrounded by brighter stars in the form of a half -circle. The whole looks like a nebula in a small instrument, but a larger telescope sh^ws the stellar formation of the group. R. A. VIII h. 46 m.; D. + i2° 10'. This cluster is listed in some atlases as 17 12; or 2682. 60. — Ca'-nes Ven-at'-i-ci, the Hunting Dogs. (Maps, all northern except pp. 39, 59, also pp. 49, 53. N. H., R. A. XIII h.; D.+40°.) A small modern constellation, near handle of the Great Dipper, or Plough. 61. — Double star marked 12; Alpha (a) in some atlases. An easy object for very small instruments. This star was named by Halley "Cor Caroli" (the heart of Charles) in honor of the English monarch, Charles II. Mag. 2.9 and 5.4; A white, B blue; distance = 2o"; p.=227°; R. A. XII h. 51.4 m.; D.-f-38° 52'. 62. — The star marked 75 forms a wide double, easily divided by an opera-gla.ss ; the companion star is registered as 77; mag. 6.2 and 6; distance = 290"; p. =297°; R. A. XIII h. 5.1 m.; B.+ 39° 4'- 63. — The nebula M 51, listed sometimes as 1662, or 5194, is illustrated on p. 11; but it is beyond the range of small instruments. R. A. XIII h. 26 m.; D. -1-47° 43'. 64. — This cluster, marked M 3 (5272), is not so beautiful in structure as the preceding object, but is within range of small instruments. So seen, however, its appearance is nebulous, showing little brilliancy. R. A. XIII h. 38 m. ; D.+28° 53'. 6s. — Ca'-nis Ma'-jor, the Great Dog. (Maps, pp. 45, 41, 49. N. H., R. A. VII h.; D.-20°.) A fine constellation, southeast of Orion. 66. — vSi'-rius, the Alpha (a) of this constellation, bluish white in color, is by far the brightest star in the heavens, being of magnitude — 1.6, and having about 12 times the brilliancy of Aldebaran or about 13 times that of Pollux or Spica. Its intrinsic luminosity exceeds that of our Sun by 20 times. It is also the nearest of the stars visible to the unaided eye from the latitudes of Europe or N. America. It is at a light-distance of 8.7 years. The small star 61 in Cygnus was for a long time considered nearer than Sirius, but this is now known to be an error. Sirius represents, according to the spectroscope, a type of stars less advanced in development than our Sun, but older than the " Orion " stars ; see [290] . Its proper motion is I ".32 a year, equivalent to 10.3 miles a second, or over 36,000 miles an hour. The distance of J 22 21 ^Beginner's Star«*BooFi the star is such, however, that — although it is relatively so near — it takes a century of time for it to move through a space on the celestial sphere equivalent to -ri the apparent diameter of the moon. Its radial velocity (its velocity in the line of sight) is 300 miles a minute in the direction of our solar system. As Sirius is the leading star of the constellation, the Great Dog, it is sometimes called the Dog Star, and the days, July 25 to Sept. 5, when Sirius rises at nearly the same time as the Sun, are called "the dog days." And Homer's "Dog" was the star Sirius, always conspicuous in the night skies of autumn and winter. "The autumnal star, whose brilliant ray- Shines eminent amid the depth of night. Whom men the dog-star of Orion call." For Sirius was also frequently represented as the hunting dog of the Giant Hunter (see [290] ). Sirius has a faint companion star, invisible except in large instruments. R. A. Vlh. 40.7 m.; D.-i6°35'. 67. — Star-cluster M 41, a fine spectacle in small instruments. R. A. VI h. 41.8 m.; D.— 20° 38'. 68. — Double star, Mu (/"), mag. 5.2 and 8.9; A yellow, B gray; distance = 2 ".5; p. =340°; R. A. VI h. 51.5 m.; D.-i3° 55'. This star not included in Night Charts ; but easily found by ref. to its Right Ascension and Declination in N. H. Map at close of book. 70. — Ca'-nis Mi'-nor, the Little Dog. (Maps pp. 45, 41, 49. N. H., R. A. VII h. 27 m.; D.-|-7°.) A small but ancient constellation, north of Canis Major, and containing one first magnitude star. 71. — Pro'-cy-on, "the precursor of the Dog"; or the star which precedes or goes before the Dog-Star, i. e. Sirius. Procyon is a star of the first magnitude and has, like Sirius, a faint companion. Like Sirius also it is one of the nearest of the brighter stars, being at a light- distance of 10 years. In its general nature or type it is midway between Sirius and our Sun. It has a proper motion of i ".25. It is approach- ing our system at the rate of 150 miles a minute. R. A. VII h. 34.1 m.; D. + 5° 29'. 72. — The little star marked 14 is a triple; mag. 5.5, 7, and 8; A white, B bluish, C blue; A-B, distance = 76", p. = 66°; A — C, distance = 112", p. = 153°; R. A. VII h. 53.2 m.; D.+2° 29'. Ca-no'-pus, see [27]. Ca-pel'-la, see [36.] 75. — Cap-ri-cor'-nus, the Sea-Goat. (Maps pp. 57, 61. N. H„ R. A. XX h. 50 m.; D.- i8°.) A constellation of small stars, but important because lying in the Zodiac or pathway of the planets. 76. — The star Alpha («); name Giedi; a re- markable object, comprising at least six com- ponents. The two larger can be seen by a keen eye, unaided, or by a poor eye with assistance of opera-glass. Each of these is a triple; the four larger stars of the group are as follows: a', mag. 3 and 9.5; a', mag. 4 and 9; color of two chief stars, yellow; a^-a", distance = 376".!; p. =291°; R. A. (of a') XX h. 12. i m.; D. - 12° 49'. 77. — Beta (/S), an easy but pretty double; mag. 3.2 and 6.2; A orange, B blue; distance = 205"; p. =267°. R. A. XX h. 15.4 m.; D.- 15° 6'. Arabic name, Dabih. 78. — Omicron (o) is also an easy double, though more difficult than the last; mag. 6.1 and 6.6; A white, B bluish; distance = 22 " ; p. = 240°; R. A. XX h. 24.2 m.; D.-i8° 55'. 79. — Pi (tt), a double star; mag. 5.1 and 8.8; A pale yellow, B bluish; distance = 3 ".5; p.= 146°; R. A. XX h. 21.6 m.; D.-i8° 32'. 79b. — Rho (p), a close double star; mag. 5 and 7.5. A white, B yellow; distance = 3"; p.= 173°; R. A. XX h. 23.2 m.; D.-i8° 9'. For location, see N. H., at the position just in- dicated. Ca-ri'-na, see Argo Navis [25]. 80. — Cas-sio-pe'-ia. (Maps, all northern, p. 39, etc. _N. H., R. A. I h.; D.+6o°.) A rich and interesting constellation of the northern sky, directly across the Pole from Ursa Major. In the mythical history of the group, Cassiopeia was the mother of Andromeda; see [i] in this Catalogue. 81. — Alpha (a); a fine double, though the be- ginner may have difficulty just at first in detect- ing the smaller component. The primary star is variable, being 2.2 mag. at its brightest. Mag. of companion 9; A reddish, B blue; dis- tance = 62"; p. =280°. R. A. o h. 34.8 m.; D.-|-55° 59'. Arabic name, Schedir. 82. — The star Eta (r/) is one of the most famous binaries. There is much difference among observers as to the colors. They are probably yellow and red, bat the smaller star seems purple in small instruments. See p. 16. Mag. 3.7 and 7.6; distance = 5".6; p. = 223°; R. A. oh. 43 m.; D.+57° 17'. 83. — Iota (z), a triple star; mag. 4.8, 7.1, and 8.1; A yellow, B blue, C blue; A-B, distance = 2".2, p. = 254°; A-C, distance = 7", p. = iio°. R. A. II h. 20.8 m.; D.-f66° 57'. A 3-inch telescope will usually show only two com- ponents. Cas'-tor, see [186]. 90. — Cen-tau'-rus, the Centaur. (Maps pp. 49 and 53; and S. H., R. A. XIII h.; 0.-50°.) A large and brilliant constellation, visible, for the most part, only from latitudes near -or south of the equator, but some of its northern- most stars can be seen in our evening skies of an ©bserver's Catalogue 123 June and July. Centaurus has two first-mag. stars , Alpha ( a) and B eta ( /O) . The latter is not among the nearest of the very bright stars, its distance being 88 light-years; it has a small proper motion of o".o4 per year. Qi; — Alpha (a) is the nearest of the fixed stars, being at a light-distance of only 4.3 years. It is also a binary, the two components com- pleting their period of revolution in a Httle over 81 years. The brighter component of the system, called a^, matches our Sun very nearly in size and in constitution. The proper motion of the pair is 3".66 ; they are approaching us at a velocity of 13.7 miles a second. 100. — Ce'-phe-us. (Maps, all northern; N. H., R. A.XXII h.; D.-|-73°.) A northern con- stellation, on the other side of the Pole from the Great Dipper. For the story of Cepheus, see Andromeda [i]. loi. — The star Delta (6) is variable in magni- tude; maximum, 3.7; minimum, 4.6; period 5d. 8h. 47m. 39s. It is also an interesting and easy double for very small instruments. Mag. of smaller star, 7.5; A deep yellow, B blue; distance = 4i";p. = i92°; R. A. XXII h. 25.4m.;D.+57°54'. 102. — Beta (p), a double star; mag. 3.3 and 8; A white, B blue; distance = 13". 5; p. = 250°; R. A. XXI h. 27.4 m.; D.+70° 7'. Arabic name, Afphirk. 103. — The star Xi (S) is also an easy double, easier for a 2-inch telescope than the preceding. Mag. 4.4 and 6.5; colors, both bluish; distance = 6"; p. = 285°; R. A. XXII h. 0.9 m.; D.+ 64° 8'. 104. — The star Mu (m) was called by Sir William Herschel a "garnet" star, because of the intensity of its red color. In order to appreciate its peculiar hue, some white star, like the Alpha {a) of Cepheus, should be com- pared with it at the time. R. A. XXI h. 40.4 m.;D.+58° 19'. no. — Ce'-tus, the Whale. (Maps pp. 61, 41. N. H., R. A. I h. 35 m.; D.-io°.) A large constellation lying westward from Orion and south of Aries and Pisces; see [i]. III. — ^Alpha (a), a second mag. star, yellow, with a blue star of the 5.5 mag. in same field; use low power. Not a true double, but an interesting object. R. A. II h. 57.1 m.; D. -1-3° 42'. Arabic name, Menkab. 112. — Gamma (y), a fine double star for a 3- inch telescope; mag. 3.7 and 6.2; A yellow, B blue; distance = 2 ".5; p. = 290°; R. A. II h. 38.1 m.; D.-f2° 49'. 113. — Omicron (o), one of the most remarkable of the variable stars; R. A. II h. 14.3 m.; D. — 3° 26'. Its name is Mira = the Wonderful. The variability of the star was discovered by F'abricius in 1596. " In 1779 Herschel saw the star when it was nearly as bright as Aldebaran, while 4 years later it was not visible even through his telescope. This means that at maximum it was at least 10,000 times as bright as at miminum. Ordinarily its maximum is much below that observed by Herschel and its mini- mum considerably above. . . . Three hun- dred years have only added to the mysteries associated with its behavior." — Moulton, In- trod. to Astronomy, p. 531. See, also, p. 14 of this volume. 114. — Zeta (C) optical dbl. ; mag. 3.5 and 9; distance =185"; p. =41°; R. A. I h. 46.5 m; D. — 10° 50'. Arabic name, Baten Kaitos. 116. — Double star, marked 66; mag. 5.7 and 7.8. A pale yellow, B blue; distance = i6".6; p.=230°; R. A. II h. 7.7 m.; D.-2° 52'. Co-lum'-ba ; see [125]. 120. — Co'-ma Ber-e-ni'-ces, Berenice's Hair. (Maps, pp. 49, 43, 53, 55; N. H., R. A., XII h. 40 m.; D. -f24°.) A small but interesting group lying between Leo and Bootes. It is in the nature of a scattered cluster, not conspicu- ous to the naked eye but extremely pretty in opera-glass, in field-glass of large aperture, or in small telescope with low-power eyepiece. According to the ancient myth, Berenice — Queen of one of the Ptolemies of Egypt, 3d century B.C. — sacrificed her beautiful locks as a thank-offering for one of her husband's victories. Her hair, when shorn, was entrusted for keeping to one of Egypt's temples. From this it was stolen. The queen bitterly la- mented the loss, and blamed the keepers of the shrine. They assured her, however, that Jove had placed her locks, for greater honor, in the skies; and they pointed out to her among the stars those strands and braids of twinkling light which we now know as " Coma Berenices. " A very beautiful nebula, numbered in some lists as H. V. 24 (in others as 3106); is illustrated on p. 15. Unfortunately, it is not impressive in small instruments. R. A. XII h. 31.4 m.; D. -f- 26° 32'. 121. — The cluster marked M 53, noted in some atlases as 3453 or 5024, is also not brilliant in a small telescope. R.A.XIIIh.8m.; D.-|-i8°42'. 125. — Co-lum'-ba, the Dove. (Maps pp. 41, 45. S. H., R. A. V h. 50 m.; D.-37°). A small constellation, located below Lepus and to the west of Canis Major. Its brightest star, Alpha («), mag. 2.8, is called Phact. 130. — Co-ro'na Bo-re-al'-is, the Northern Crown. (Maps pp. 47, 59. N. H., R. A. XV. h. 35 m. ; D.-f30°). A constellation lying between Bootes and Hercules, forming a crown or chap- let of small stars; very beautiful as a group. The brightest star, Alpha {a), mag. 2.3, is called Gemma, the Jewel [of the Crown]. 124 H Beginner's Star^Booh 131. — The star Zeta (C) is a pretty double; mag. 6 and 5; A white, B blue; distance = 7".5; p. = 305°. R. A. XV h. 35.6 m.; D.+36° 58'. 135. — Cor'-vus, the Raven, or the Crow. (Maps PP- 49. 53- N. H., R. A., XII h. 20 m.; D.— l8°.) A small but clearly marked constella- tion lying between Hydra and Virgo. The two upper stars of Corvus point toward Spica, the first-magnitude star of Virgo, and form an interesting special group, see p. 26. 136. — The star Delta (tJ) is an 'easy but pretty double; mag. 3.1 and 8.4; A yellow, B purple; distance = 24". 5; p. = 214°. R. A. XII h. 24.7 m.; D. — 15° 58'. Arabic name, Algorab. 140. — Cra'-ter, the Cup. (Maps pp. 49, 45, 53. N. H., R. A. XI h. 20 m.; D.-I5°.) A small constellation of small stars lying between Hydra and Corvus. The stars form the out- line of a chalice or cup. The group contains few objects of telescopic interest. 143.— Crux, the Cross. (S. H., R. A. XII h. 30 m. ; D. — 60°.) A small constellation near the south celestial Pole, remarkable for the "Southern Cross," a strikingly beautiful figure formed by its four brightest stars, one of which, Alpha (a), is of the first magnitude; see p. 140. This star is at a distance of 59 light-years, and has a proper motion of o".o6. 145. — Cyg'-nus, the Swan. (Maps pp. 39, 51, 57. N. H., R.A.XXh.2om.;D.+4i°.) Lying within one of the most impressive sections of the Milky Way, Cygnus contains many objects of interest and beauty. The stars Alpha (a), Beta (/O), Delta ((5), Epsilon (e), and Gamma (y) form the figure of a cross, and the group is often called the "Northern Cross" as dis- tinguished from the "Southern Cross," noted above. The stars of the northern group, while not so brilliant as those of the southern, form an even clearer figure of the cross, because of the presence of a star, Gamma (y), near the intersection of the beams. One of the most beautiful nebulas of the constellation is shown on p. 8; but it is unfortunately beyond the range of the average telescope. 146. — The brightest star of the constellation. Alpha (a), or Den'-eb, is a star of the first magnitude (1.33), though one of the most remote among all the bright stars of the sky. It seems far less brilliant to us than Sirius, but its distance from us is so much greater that Newcomb estimates its actual luminosity as exceeding that of our Sun by at least a thousand times. It is distant from us more than 400 light-years; its parallax being imperceptible and its proper motion being also very small (see tables, pp. 138 and 139). In spite of its vast distance, we know from the spectroscope that it is a star of the same general type as Sirius, although probably more advanced in develop- ment. R. A. XX h. 38 m.; D. -1-44° 55'- 147. — The star marked Beta (/5) is given the name Al-bi'-re-o. It is one of the finest doubles for small instruments; mag. 3.2 and 5.4; A orange, B blue; distance = 34".3; p. = 55°.7; R. A. XIX h. 26.7 m.; D.+27° 45'. No physical connection has been detected; the star is prob- ably not a binary. 148. — The star marked Omicron (o) has an- other quite near it, marked in many atlases 0^. They form an easy group for an opera-glass or field-glass. In a 2-inch or 3-inch telescope a companion to o^ will be seen, and in a 6-inch instrument there appears still another com- ponent. This star, however, is very small, be- ing rated as nth or 12th magnitude. The three components visible in a small instrument are o', mag. 5; o^, mag. 4; and the brighter companion of o^, mag. 7. A and C are blue in color; B, or o^, orange; A-B, distance = 337". 8; p. =323°. 7; A-C, distance = io6".8; p. = 173°. 5; R. A. of o^, XX h. 10.5 m.; D.+46° 26'. 149. — The star marked J2 is listed in some atlases as a double. This is an error, due to confusion with one of the components of the preceding object. But it is in the same inter- esting low-power field. R. A. XX h. 12.4 m.; D.+47°24'. 150. — This small object, marked 61, is one of the most interesting doubles in the sky, — the first star whose distance from our sun was accurately measured. Bessel (1838) found a parallax of o".3i, indicating a light-distance of 105 years. This was later superseded in general estimation by Auwers' parallax of o".56, indicating a light-distance of 5.8 years, and making the star the nearest in the northern hemisphere. Statements to this effect appear in many current volumes of astronomy. But it has recently been determined that Bessel's original result was far nearer to the fact; the parallax of o".3ii is now generally accepted. The light-distance of the star is thus 10.5 years ; it is not so near as Sirius, but one of the nearest in our sky. See the table of star- distances, p. 139. The magnitudes of the components are 5.6 and 6.3; both yellow in color; (1905) distance = 22".5; p. = 127°; R. A. XXI h. 2.4 m.; D.-h38° 15'. 151. — This star, which we mark Chi (,r) is marked in some atlases as x ^ and the next star, 77, is then marked x '• The former star, which we mark simply x, has a distant companion, but it is chiefly remarkable as a long-period variable. For six months at a time it remains invisible to the unaided eye. Its "period" is 406 days. In about 3I months it increases from its minimum brightness, mag. 13.5, to maximum. Its maximum, as in the case of the Omicron (") of Cetus, is by no means uniform, an ©bserver's Catalooue 125 — ranging from mag. 6.5 to 4. Its color is a fine red except that its color-intensity decreases with its increasing brightness. R. A. XIX h. 46.7 m.; D.+32° 40'. 152. — The star marked 27, sometimes called X\ is an easy double for small instruments; mag. 5 and 8; A yellow, B blue; distance = 26"; p. = 73°; R. A. XIX h. 42.6 m.; D.+33° 30'. 153. — Mu (/i) is a triple; two of the components being almost inseparable in a small instrument, and the third, and smaller, star more distant. Mag. 4.7, 6, and 6.7; A white, B blue, C blue; A-B, distance = 2", p. = 125°; A-C, distance = 217", p. = 61°; R. A. XXI h. 39.6 m.; D.+28° 18'. 154. — The star cluster M 39 is well worth finding. It is on a line from Beta (/3) to Gamma {y), continued about 14° onwards. R. A. XXI h. 28m.;D.+48°9'. 155. — Del-phi'-nus, the Dolphin. (Maps pp. 57, 61, 51. N. H., R. A. XXh.4om.; D. + i2°.) A small but finely marked constellation lying south of Cygnus and east of Aquila. 156. — The star Alpha (a) is a wide double; mag. 4 and 9.5; distance = 35"; p. =278°; R. A. XX h. 35 m.; D. + 15° 34'. 157. — The star Gamma ( y) is of special inter- est and beauty in a small instrument. Mag. 5.5 and 4.5; A yellow, B bluish-green; dis- tance = 12"; p. =274°; R. A. XX h. 42 m.; D.-h 15° 46'. Den'-eb, see [146]. 160. — Dra'-co, the Dragon. (Maps, all north- ern, pp. 39, etc. N. H., R. A. XV h. 55 rh.; D.+7o°.) 161. — This star, Alpha (a), is chiefly interesting because of its former position — 4000 years ago — as the Pole Star. Its ancient name was Thu'-ban. The Pole is now near the star Polaris in Ursa Minor. See [406]. For expla- nations of such phenomena, see any one of the text-books on Astronomy noted on p. 145. R. A. XIV h. 1.7 m.; D.-f 64° 51'. 162. — Nu {y) is an easy but beautiful double, even for opera-glass and field-glass. Mag. of both components, 5; color, gray; distance = 6i".7; p.=3i3°; R- A. XVII h. 30.2 m.; D.+ 55° 15'- 163. — Omicron (o) is another double. Mag. 4.8 and 7.6; A yellow, B lilac; distance = 32"; p. = 340°; R. A.XVIIIh.49.7m.; D.+59°i6'. 164. — This star, Iota (z), is also a double though more difficult than the star just mentioned. Mag. 3.5 and 9; A orange, B yellow; distance = 254".6; p. =50°; R. A. XV h. 22.7 m.; D.-f- 59° 19'- 165.— Gamma {y) may possibly require a 3I or 4 inch telescope for its satisfactory obser- vation, as the companion star is even smaller than in the preceding pair. Mag. 2.4 and 12; distance =124". 7; p. = 116°; R. A. XVII h. 54.3 m.; D. + 5i° 30'. Arabic name, Etamin. 166. — Delta (S) is also a wide double and the companion is less diSicult. Mag. 3 and 9.5; A yellow, B red; distance = I54".7; p. = 27°. 7; R. A. XIX h. 12.5 m.; ^.+67° 29'. 170. — Equu'-le-us, the Little Horse (see N. H., R. A. XXI h. 10 m. ; D.+5°), a small unimpor- tant constellation lying between Delphinus and Pegasus. See the map of the N. H. at the close of this volume, at R. A. just indicated. 175. — E-rid'-a-nus, the River. (Maps pp. 41, 45. N. H. and S. H., R. A. Ill h. 40 m.; D.— 25°.) A long line of stars starting near Rigel in Orion and flowing westward and south- ward toward Cetus and Fornax. Few telescopic objects of interest, but it contains one first- magnitude star. Alpha (a), or Achernar (A'- ker-nar), visible only in far southern latitudes. See tables, pp. 139, 140. 176. — This star marked w is sometimes classi- fied as J2. The contrast in the colors of the components is peculiarly fine. Mag. 5 and 6.9 ; A yellow, B blue; distance = 6".7 ; p. =345°; R. A. Ill h. 49.3 m.; D.-3° 14'. 177. — Gamma (/) is a good double for a 3-inch, though the companion — not to be confused with the small 6-mag. star in the same field — is rather small. Mag. 2.5 and 10; A yellow, B pale gray; distance = 51 ".6; p. = 238°; R. A. Ill h. 53.4 m. ; D. — 13° 48'. Arabic name, Zau- rak or Alhena. Fo'-mal-haut, see [331]. 185. — Gem'-in-i, the Twins. (Maps pp. 45, 41, 49, 39. N. H., R. A. VII h.; D. + 22°.) One of the most interesting and important of the constellations. The two brightest stars. Cas- tor and Pollux, even in prehistoric times, were suggestive of a pair — so near are they together and so conspicuous in brilliancy. Many have been the legends, even among savage peoples, in which these stars have been identified with heroic groups. But the most familiar to us is that which has given them the names of the warrior brothers, sons of Jupiter and Leda, whom Macaulay celebrates in his stirring poem, "The Battle of Lake Regillus." 186. — The star Castor, marked Alpha (a) in all star maps, is a double star, a binary, — a fine object for a 2-inch or 3-inch telescope; mag. 2 and 2.9; colors, both greenish white; distance = 6"; p. = 225°; R. A. VII h. 28.2 m.; D.+32° 6'. It is also interesting to know that both components are spectroscopic binaries (see table of spectroscopic binaries on p. 143), and that at a distance of 73" is another com- ponent, mag. 9, visible only in larger instru- ments. The parallax of Castor (o".028) makes its distance about 116 light-years. Both of 126 a Beginner's Star»»ffiook the main components of Castor are "Sirian" stars, see [66.] 187. — Beta (p) or Pollux is a multiple star of at least 6 components, most of them at con- siderable distance from the primary and too faint for easy observation. Three may be seen in a telescope of 3 to 3I inches. Mag. 2, 9, and 9.5 "^ A orange; A-F, distance = 242", p.= 75°; A-E, distance = 2 19", p. = 90°; R. A. VII h. 39.2 m. ; D.+28° 16'. Pollux is brighter than Castor, although assigned the letter Beta (/j). It is nearer, also; its distance is 51 light- years. It has a yearly proper motion of o".62. In its physical constitution it exactly resem- bles Arcturus [41]. It is slowly receding from our system. 188. — The fine star-cluster marked M 35 — beautiful even in a good field-glass and visible in an opera -glass — is a fine object in a small telescope. Its existence, under good atmos- pheric conditions, can be detected with the unaided eye. R. A. VI h. 3 m.; D.-|-24° 21'. 189.— Kappa («), though not a large star, is an extremely pretty double in a 3-inch glass. Mag. 3.7 and 8; A orange, B pale blue; distance = 6".4; p. =235°; R. A. VII h. 38.4 m.; D.+24° 190. — Delta ((5) is an easier double than the preceding. Mag. 3.7 and 8; A yellowish, B red; distance = 7"; p. = 210°; R. A. VII h. 14.2 m. ; D.-f22° 10'. Arabic name, Wesat. 191. — EpsUon (f) is also a double star. Mag. 3.2 and 9.5; A white, B blue; distance =110". 6; p. = 94°; R. A. VI h. 37.8 m.; 0.-^25° 14'. Arabic name, Mebsuta. 192. — Lambda (A) is a double star, mag. 4, unmarked by any letter in Key-Maps, just below Delta (S) and Zeta (C) and forming a small triangle with them. It is a little difficult for any telescope smaller than a 3|-inch, but is worth trying with a 3-inch on a clear night. Mag. 3.7 and 10; A white, B yellowish; distance = 10"; p. = 30°; R. A. VII h. 12.3 m.; D.-Fi6° 43'- 193. — Zeta (Q is itself a double star, and is an easy object even in a 2-inch instrument. Mag. of brighter star varies from 3.7 to 4.3; smaller component, about 7 ; A yellow, B blue ; distance = 94"; p. =350°; R. A. VI h. 58.2 m.; D.+20° 43'. Arabic name, Mekbuda. 194. — The small star Nu (y) is here inserted not only because it is a double, but because of its historic interest. It was near this star that Sir William Herschel discerned the ob- ject which he found to be an unknown planet, a discovery which — to human knowledge — doubled the diameter of the solar system. Ura- nus, as it came to be called, is over twice as far from the sun as Saturn, the remotest planet then known. The components of the little star Nu (v) are mag. 4 and 8; distance =113"; p. =330°; R. A. VI h. 23 m.; D. -|-20° 17'. 200. — Her'-cu-les. (Maps pp. 53. 47. 57. 59; N. H., R. A. XVII h. 20 m.; p.-|- 30°.) A large and important constellation lying be- tween Lyra and Corona Borealis, and south of Ursa Major. The group is not easily recog- nized at first, but when once learned it becomes strikingly clear and interesting. The hero, as usually drawn, is supposed to be kneeling; his head at Alpha (a), shoulders at Beta (/j) and Delta ((5), belt at Zeta (C) and Epsilon (f); one knee at Rho (p) and one at Eta (tf). In early lists, the constellation is often called the Kneeler. The easiest method for noting and identifying the group is indicated on p. 46. 201. — Alpha (a) is a double star of especial charm and beauty. As the larger component is variable in brilliancy, the star will be found easier to divide at some seasons than at others. It can be divided, however, by a 3-inch, and sometimes by a 2-inch. Mag. (about) 3.5 and 5.4; Ayellow, B blue; distance = 4".8; p. = 113°; R. A. XVII h. lo.i m.; D.-fi4° 30'. Arabic name, Ras Algethi. 202. — Delta (<5) is an easier double than the above, if the air be clear and the night moonless. Mag. 3.2 and 8; A greenish, B bluish; distance = 15"; p. = 195° ; R. A. XVII h. 10.9 m. ; 0.-^24° 57'. 203. — Mu (j^); — Mag. 3.5 and 8; A yellow, B blue; distance = 31 ".5; p. =245°; R. A. XVII h. 42.5 m.; D.-|-27° 47'. 204. — Rho (p) is a double, unusual in its color- ing, the components being white and green. Mag. 4.5 and 5.5; distance = 4"; p. = 312°; R. A. XVII h. 20.2 m.; D.-|-37° 14'. 205.— This star, marked 95, is also peculiar in the coloring of its components, one being red and the other green. It is not a difficult object, even for a good 2-inch, but it is small and not easy for the beginner to find. Mag. 5.1 and 5.2; distance = 6"; p. = 262°; R. A. XVII h. 57.2 m.; 0.-^21° 36'. 206. — The star-cluster M 13 is one of the most remarkable in the sky, comprising over 5000 stars. Sir Wm. Herschel's estimate of 14,000, though naturally suggested by the splendor of the central mass, was probably too large. Halley, who discovered it in 17 14, reported it as one of six "nebulas," — all that were known in 17 16. Before 50 years had passed. Messier had added nearly 100, and by 1830 the three Herschels (Sir William, Sir John, and Caroline) added more than 3000, counting both nebulae and star-clusters. These were at first classified together, — ^for the nebulfe were generally regarded as star-clusters too distant or faint for the stars to be resolved by the telescope. We now know that the two classes of objects are distinct in character, see p. 19. M 13 is visible even in a 2-inch telescope, though its real interest and splendor cannot easily be gathered from an instrument less than an ©bserver's Catalogue 127 6 inches in aperture. R. A. XVI h. ^g.i m.- D.+36°39'. 207. — The star-cluster marked M 92 Has almost on a line between Pi {n) in Hercules and Beta (^) in the head of Draco. Easily visible, but with the appearance of a nebula, in small in- struments. R. A. XVII h. 14 m.; D.-f 43° 15'. 208. — Gamma {y), a double star; mag. 3.8 and 8; A white, B lilac; distance = 40". 5; p. = 240°; R. A. XVI h. 17.5 m.; D.+ ig"" 23''. 209. — Kappa (w), shown only in N. H., s. west of Gamma (7). An easy double for very small instruments. Mag. 5.1 and 6.1; A yellow, B reddish; distance = 3 1 " ; p. =10°; R. A. XVI h. 3.6m.;D-fi7° 19'. Hy'-a-des, see [383]. 210. — Hy'-dra, the Water-Snake. (Maps pp. 49- 45, 53- N. H., R. A. XI h.; D.-i7°.) A constellation extending through more than a fourth of the southern sky, long and winding in form but not broad. Head south of Cancer, lying between Leo and Canis Minor; the tail reaching to Scorpius. 211. — Alpha {a) is sometimes called Cor Hydrffi, or the heart of Hydra ; sometimes Al- phard, the Solitary — as it shines brightly in a region of faint stars. It is a double, but diffi- cult in anything less than a 3|-inch. Mag. 2 and 10; A orange, B green; distance = 281 ".2; p. = 153°; R. A. IX h. 22.7 m.; D.-8° 14'. 212. — Epsilon (e) is a multiple star of four com- ponents, but in a 3-inch or even in a 3i-inch not more than two are likely to be seen. Mag. 3.5 and 6.8 ; A yellow, C blue; distance = 3".5 ; p. = 230°; R. A. VIII h..4i.5 m.; D.-F6° 47'. 220. — La-cer'-ta, the Lizard. (Maps, all north- ern, except pp. 47 and 59. N. H., R. A. XXII h. 19 m. ; D.+45°.) A small, inconspicuous constellation of little importance. 221. — The star marked (? is a quadruple, but only two of the components are visible in instruments under 4 inches. Mag. 6, 6.5, 10, and 8.7; A white, B white, C greenish, D blue; A-B-, distance = 22".3; p. = 186°; R. A. XXII h. 31.4 m.; D.-|-39° 7'. 223. — Le'o, the Lion. (Maps pp. 45, 49, 53. 39, 51. N. H., R. A. X h. 25 m.; D. + i5°.) One of the noblest of the constellations ; between Cancer and Virgo; specially marked by the figure of the "sickle" formed by the stars Alpha (a). Eta (7), Gamma (7), Zeta (Q, Mu (/"), and Epsilon (f). The constellation lies in the Zodiac, — or track of the planets; and as it occupies a large part of the sky, the constel- lation-outline is often obscured or confused by one of the "wanderers." 226. — Alpha (a-) or Reg'-u-liis, its brightest star, is a double, though rather difficult for a 3-inch. Mag. 1.8 and 7.6; A white, B purple; distance = 177"; p. = 307°; R. A. X h. 3 m.; D. + i2° 27'. Regulus is reckoned a first-magnitude star, although it is less than -j as bright as Vega [261], and only xs as bright as Sirius [66]. Its small parallax indicates a distance of more than 80 light-years. The spectroscope places it among the "Orion" class of stars, for which see [290]. 227. — Gamma (7) is one of the finest of all the double stars, and one of the most impres- sive binaries. Fortunately the distance be- tween the components seems to be increasing, so that i't is becoming still more available for small instruments. Mag. 2.6 and 3.8; A orange, B yellow; distance = 3".6; p. = 117°; R. A. X h. 14.5 m. ; D.-f 20° 21'. Arabic name, Al Gieba. 228. — Tau (r) is a double so easy as to be separable by a good field-glass; mag. 5.4 and 7; distance = 90"; p. = 170°; R. A. XI h. 22.8 m.; D:+3°24'. 229. — Beta (/3) or Deneb'-ola has a small neigh- bor star: too distant for real component; mag. 2.2 and 7; A bluish, B red; distance = 1 134"; p.=20i°; R. A. XI h. 44 m.; D. + i5° 8'. 235. — Le'-o Mi-nor, the LittleXion, literally the Lesser Lion. (Maps pp. 39, 43, 45, 49, 51. N. H., R. A. X h. 20 m.; D. + 34°.) A small constellation of little importance, lying be- tween Leo and Ursa Major. 240. — Le'-pus, the Hare. (Maps pp. 41, 45. N. H., R. A. V h. 32 m.; D.-20°). A small constellation, just south of Orion. 241. — ^Alpha (or) is a little difficult for a 3-inch, but easy for anything larger — if the eye be carefully on the lookout for the dull color of the companion. Mag. 2.6 and 9; A yellow, B gray; distance = 36"; p. = 156°; R. A. V h. 28. 3 m. ; D. — 17° 54'. Arabic name, Arneb. 242. — Gamma {y) is a wide but lovely pair, so easy as to be separable even by a good opera- glass. Mag. 3.8 and 6.4; A yellow, B pale green; distance = 95"; p.=35o°; R. A. V h. 40.3 m.; D.— 22° 29'. 244. — Beta (/?), a rather difficult triple, except in instruments of 3^ inches and over. Mag. 3, 10, and 11; A-B, distance = 3", p. = 300°; A-C, distance = 66"; p. = 146°; R. A. V h. 24 m.; D. —20° 50'. Arabic name, Nihal. 245. — Li'-bra, the Scales, or the Balances. (Maps pp. 53, 49, 57. N. H., R. A. XV h. 8 m.; D. — 13°.) A small constellation lying in the Zodiac or track of the moon and planets; between Virgo and Scorpius. 246. — -Alpha {a) is a wide double, easily divided by field-glass or opera-glass; mag. 2.9 and 5.3; A yellow, B gray; distance = 23o".8 ; p. =314°; R. A. XIV h. 45.2 m.; D.-i5° 35'. Arabic name, Zuben el Genubi, the southern scale. 128 a Beginner's Star»»Booft 247. — Beta (/3), not double in a small telescope, but the star is interesting because of its pale- green color. Mag. 2.7; R. A. XV h. 11.6 m. ; D.— 9° i'. Arabic name, Zuben el Chamali. 248. — Iota (z) is a double but not easy even in a 3-inch. A4ag. 5.5 and 9.5; A yellow, B purple; distance = 57". 5 ; p- = 1 10°. 5. The smaller com- ponent is also double in a larger instrument. R. A. XV h. 6.5 m. ; D. - 19° 25'. 250. — Lu'-pus, the Wolf. (Maps pp. 52, 53. S. H., R. A. XV h. 20 m.; 0.-40°.) The reader should use the map of the S. H. for a view of the whole; the name not appearing in the smaller maps. A constellation lying directly south of Scorpius. Few of its stars ever rise sufficiently high in Europe or the United States for satisfactory observation. 251. — Xi (5') is an easy double, even in a 2- inch telescope. Mag. 5.4 and 5.7; distance = II"; p. =48°; R. A. XV h. 50.5 m.; 0.-33° 4o'. 252. — Eta (v) is also a double, though not quite so easy as the preceding. Mag. 3.6 and 7.8; distance=i5"; p.=2i°; R. A. XV h. 53.5 m.;D.-38°7'. 255.— Lynx, the Lynx. (Maps pp. 39, 43, 51. N. H., R. A. VIII h.; D.+45°.) An incon- spicuous constellation, of little importance, lying between Ursa Major and Gemini. 256. — The star marked ig is an easy and pretty triple. It is on a line from Polaris to Pollux, about 25° from the former, though the beginner will not find it readily. Mag. 6.5, 6, and 8; A white, B and C purple; A-B, distance = I4".3, p. = 3i2°; A-C, d.=2i5", p.=358°; R.A. VII h. i4.7m.;D. + 55°28'. 260. — Ly'-ra, the Lyre. (Maps pp. 57, 59, 47, 51, 61. N. H., R.A. XVIII h. 30 m.; D.+36°.) A constellation small in size but peculiarly rich in interest, lying between Cygnus, Draco, and Hercules. 261. — Alpha {a) or Vega — sometimes written Wega — is one of the brightest of the first- magnitude stars, bluish-white in color, and — according to the chemistry of the suns — in the vigor of stellar youth. Vega is of special interest to us for at least three reasons. First, it is in the general direction of this star that our solar system seems to move in the depths of space, though the exact point lies within the bounds of Hercules; see the note on p. 66. Secondly, we may remember that while Alpha {a) in Ursa Minor is at present our Pole-star, being the nearest of the bright stars to the actual polar-point of the heavens, yet this polar-point is slowly shifting its position. We have already seen that 4000 years ago this point lay near Alpha (a) in Draco. See [161].. In the time of Hipparchus' (c. 136 b. c.) it was about 12° from our present Pole-star.; it is now distant from it about i|°; it will gradually come nearer to it and in. the next century will be only i' of arc distant. This distance will then increase; at length it will approach Deneb — the brightest star in Cygnus — and then, about 12,000 years hence, it will be nearer to Vega than to Deneb, and Vega will be the Pole-star. Thirdly, it is of interest to know that Vega has a companion — rather difficult for a 3-inch, because of the extreme brilliancy of the primary, but available with a 3|-inch or 4-inch telescope. Mag. o.i and 10; A bluish white, B deep blue; distance = 43"; p. = 140°; R. A. XVIII h. 33.6 m.; D.-f38° 41'. The distance of Vega from our system is 35 light- years; its proper motion, ■o".35. 262. — Beta (^) is a variable star; its period, 12 days, 21 hours, 47 minutes, and ranging from mag. 4.1 to 3.4. It is also a triple star in a 3-inch instrument and an easy double for a 2-inch. Mag. of two of components, 6.7 and 9.2; A-B, distance = 46", p. = 150°; A-C, dis- tance =67".2, p. = 318°; R. A. XVIII h. 46.4 m.; D.-j-33° 15'. Arabic name, Sheliak. 263. — Epsilon (f) is a famous double double. An opera-glass will show it double, a telescope of from 3 to 2)2 inches (depending somewhat on the eye of the observer and the quality of the object lens) will show each of these components to be itself a double. The beginner will need a high power, but the use of a power too high will make the field of view so small that both pairs cannot be kept in the field of the instru- ment. Each of these pairs is a binary, the two components revolving about a common centre of gravity; and the pairs in turn are probably also in slow revolution about a common centre of the whole system. We have perhaps a similar system in Castor (see [186]) though in that case the components of the two larger stars are too close together for separation in a telescope. In some atlases, Epsilon (f) in Lyra is classified as two stars, «' and e^ or s and 5. The four components are as follows: «', mag. 5 and 6; f^ mag. 5 and 5; «' yellow, «=', white; e'-f", distance = 207"; p. = 173°; R. A. XVIII h. 41 m.; D.+39° 34'. 264. — Eta {rf) is a double star, though rather small for easy finding. Mag. 4.8 and 8; A blue, B violet; distance = 28"; p. = 84°; R.A. XIX h. io.4m.;D.+38°58'. 263. — Zeta (C), an easy and pretty double whether for a 2-inch or a 3-inch. Indeed a good field-glass, steadily held, will divide it. Mag. 4.3 and 5.9; A yellow, B greenish; dis- tance =44"; p. = 149°; R. A. XVIII h. 41.3 m.;D.+37°3o'._ 266. — Delta {S) is also a wide double, an easy object for a field-glass or a very small telescope. Mag. 4.5 and 5.5. A orange, B white; distance = 750"; R. A. XVIII h. 50.2 m.; D.+36° 51'. 267. — Between Gamma {y) and Beta (/?), anf* Hn Otieerver's Catalogue 129 somewhat nearer the latter star, lies M 57, the famous "Ring Nebula," interesting but not impressive in a small telescope. R. A XVIIIh. 49m.;D.+32°53'. Mi'-ra, see [113]. Mi'-zar, see [401]. 270. — M6n-6'-cer-6s, the Unicorn. (Maps pp. 45, 49. N. H., R. A. VII h. 20 m.; D.-4°.) A large constellation of inconspicuous stars, lying between Orion and Hydra. 271. — The star Beta (A), sometimes marked 11, is a fine triple. Mag. 4.7, 5.2, and 5.6. White; A-B, distance = 7"-5, P- = I33° ; A-C, distance = 3".i, p. = 108°; R. A. VI h. 24 m.; D.-6° 58'. 272. — Epsilon (£) is an easy double; the field of stars in which it lies is especially fine. Mag. 4.5 and 6.5; A yellow, B blue; distance = 14"; p. =26°; R. A. VI h. 18.5 m.;-D.+4° 39'. 273. — ^Almost on a line between Epsilon (s) and Delta ((J) will be found a star-cluster, marked in some atlases 2301, or 1465. It is in three branches. R. A. VI h. 47 m.; D.-|-o° 35'. 274. — Not far from Epsilon (t) is a pecuHarly bea utif ul cluster. It is marked in some atlases 1424, or 2244. Its general direction from the star may be noted in the Night Charts of the constellation. It is a good object even for opera-glass or field-glass. R. A. VI h. 27 m. ; D. +i° 56'. 275. — Star-cluster 1637 or 2548, fairly large, and crowded with ninth-mag. stars. R. A. Vlllh. 9m.;D.-5°3o'. 285. — 0-phi-u'-chus,theSerpent-Bearer. (Maps PP- 53- 57- N. H., R. A. XVII h. 20 m.; D.— 5°.) A large constellation, lying south- ward from Hercules and northward from Scor- pius. Its outline is peculiarly difficult to the beginner and its study may, therefore, well wait until other groups are learned. In study- ing it, remember that being able "to see the man and the serpent" is of far less importance than the ability to recognize the constellation itself as a definite group of stars. First note that the Alpha (a) of this group is brighter than the Alpha (a) of Hercules, quite near it. Take then this brighter star as the apex of the triangle. Alpha (a), Beta (/j). Kappa («). See the map on p. 53. Then trace the right- angled triangle, Beta (/3), Kappa (k), Epsilon {(). On a clear night this triangle is made more evident by noting that at each corner is a pair — Beta (/3) and Gamma (y) at one corner; Kappa (x) and Iota (0 at the next, Epsilon (f) and Delta ((?) at the third. Having learned this much of the group, the irregular line of stars from Epsilon (e) to Theta {6) is not diffi- cult. Serpens, the Serpent [365], divided by the above figure, lies in two parts — the head to the west or to the right, the tail to the east, or left; and the Serpent-Bearer, with head at Alpha («), and shoulders at Beta (0) and Kappa («), stands astride the serpent, with left hand grasping its coil at Epsilon (f), one knee at Zeta (Q and one at Eta (/;). The right hand of the figure also grasps the serpent at Nu (y) in_ Serpens. See also [365]. Ophiuchus con- tains little of telescopic interest in a small instrument. The Arabic name of Alpha (a) is Ras Alhague. 286. — The star marked 6y is an easy double even for a 2-inch. This and /'O are in an interesting field. Mag. 4 and 8; A yellowish, B purple; distance = 54".5 ; p. = 144°; R. A. XVII h. 55.6m.;D.+2°56'. 287. — The star marked 70 is also a double, though a little more difficult than the preceding. Rapidly changing binary: measures for 1911. Mag. 4.3 and 6; A yellow, B reddish; distance = 3".47; p. = 148°; R. A. XVIII h. 0.4 m.; D. + 2° 31'- 288. — In the region of Beta (/?), slightly to the northeast, is a very pretty cluster of 8th mag- nitude stars, unmarked in many of the atlases. Its place is indicated in N. H., R. A. XVII h. 40 m.; D.-|-5° 40'. 289. — A fine cluster marked in the Key-Maps as M 12. It lies on a line between Epsilon (f) and Beta (/5) ; forming almost a right angle with Epsilon (f) and Lambda (A). R. A. XVI h. 42 m.; D. — 1° 45'. 290. — O-ri'-on. (Maps pp. 41,45, 49. N. H., R. A. V h. 26 m. ; D. o°.) On the whole the richest and most impressive of the constella- tions. The mythology of the constellation has taken so many forms that it is impossible to say which should have the precedence in age or interest. The group has always, however, represented a Giant Hunter. As sings Long- fellow in his "Occultation of Orion," — " Begirt with many a blazing star Stood the great giant Algebar, Orion, hunter of the beast ! His sword hung gleaming by his side, And on his arm the Hon's hide Scattered across the midniglit air The golden radiance of its hair." According to one legend, the Giant Hunter was the companion of the Huntress Diana, who loved him and whom he desired to v:ed. Her brother, Apollo, was so opposed to their union that he caused the death of Orion by a scorpion's sting. At Diana's intercession, Orion was not only given a place among the stars, but was placed opposite to Scorpius (Scorpius always sets as Orion rises), that he might never again be troubled by the offensive reptile. The spectnim of most of the brighter Orion stars shows — despite the wide area covered — that they are much alike in physical constitu- tion and that they have, possibly, some physical connection — as if forming a loose but common I30 H Beginner's Star*Booft cluster. Betelgeuze [291] should probably be re- garded as an exception. Epsilon (f) and Gam- ma (7), Alnilam and Bellatrix, are characteristic specimens. Stars which, under spectrum analy- sis, show that they are of the "Orion type" are in the earlier stages of stellar development. They are extremely remote, most of them being at a light-distance of over 300 years, and — as is usual with the most distant stars — revealing a very small proper motion. 291. — Alpha (a), or Bet'-el-geuze, is the only marked "variable" among the first-magnitude stars, shining sometimes as a star of mag. 1.4 and sometimes as mag. 0.9 (period about 200 days), but never falling below the full first- magnitude standard. A singularly beautiful object, variously estimated as "red," a "rich topaz," a "reddish orange," etc., in color. In order to appreciate the real contrasts in star-color, the beginner should look alternately with his instrument at this star and at Rigel, or Beta (/j), of the same group. Betelgeuze is a spectroscopic binary, see p. 143. In spite of its brilliancy, it is a distant star, its light taking more than a hundred years to reach us. It has a small proper motion, o".03. It is not of the "Orion" type, but represents a later stage of development. R. A. V h. 49.8 m. ; D.+7° 23'. 292. — Beta (/S) or Rigel — pronounced Ree'-gel — is bluish-white in color, of intense brilliancy and beauty. It is one of the most remote of the brighter stars, being at a light-distance of at least 450 years. It is a double, separable, by a well-trained eye, under perfect conditions of light and air, with a 2j-inch telescope. The companion is not especially close; but so great is the brilliancy of the larger component that, in order to see the smaller, the beginner will usually need a telescope of 3I or 3I inches in aperture. Mag. 0.34 and 6.7 ; A pale yellow, B blue; distance = 9".5; p. = 200°; R. A. V h. 9.7 m. ; D.— 8° 19'. Rigel has no observable proper motion, nor motion toward or from us. In constitution it is conspicuously of the "Orion" type, tending toward the Sirian. 293. — Delta ((5), the "top star of the belt," is an easy and beautiful object in a 2-inch instrument; indeed, after the eye has had a little experience, the star can be divided even by a good 10 X field-glass. Mag. 2.5 and 6.9; A white, B violet; distance = 53"; p. = 360°; R. A. V h. 26.9 m. ; D.— 0° 22'. Arabic name, Mintaka. 294. — The star Theta {6) is a quadruple, lying within the field of the great Orion-nebula. See illustration, p. 21. The nebula itself is one of the few that may be seen with satisfaction in small instruments. Naturally enough, the larger the telescope the better the view, but even an opera-glass will indicate its existence. It shows to best advantage on a clear night when there is little or no moonlight. The nebula is composed of luminous gases, and its distance from us, and the immensity of its proportions, are so great that we can form no conception of them except in vague and general terms. It is probably at a light distance of more than 250 years, and its bounds probably exceed by many- thousand times the area inclosed by the orbit of Neptune, our outermost planet. It seems to be receding from us in space at the rate of about 600 miles a minute. The star Theta {6) is itself of great charm and interest even in a 2-inch telescope. The four components form what is called a "trapezium," an irregular quadrilateral. Mag. 6.8, 7.9, 5.4, and 6.9; A white, B lilac, C garnet, D reddish; A-B, distance = 8". 7, p. =32°; A-C, distance = 13", p. = 132°; A-D, distance = 2i", p. = 95°; R. A. V h., 30.4 m. ; D. — 5° 27'. Large telescopes show the existence of several fainter stars in the trapezium group. 295. — The star marked m is an easy double for small instruments. Mag 5 and 5.1; distance = 32";p.-28°;R. A.Vh. 17.6 m.;D. -^3° 27'. 296. — Zeta (Q, the third star of the belt, is a triple, but it is not an easy object for an instru- ment smaller than a 3j-inch. Mag. 2, 4.2, and 10; A yellow, B purple, C gray; A-B, distance = 2".8, p. = 158°; A-C, distance = 57", p.= 9°; R. A. V h. 35.7 m.; D.-2° o'. 297. — Iota (z) is the third-magnitude star just below Theta {6) in the Key-Maps. It bears no symbol, because the map here is crowded, but its identity — together with the smaller star to the right — will be evident. Iota (?) is a triple, but will appear only a double in a telescope of 3-inches or under. It is not easy with a 2-inch. The beginner will find the small* stars in this immediate region somewhat con- fusing, at the first, but will soon learn to dis- tinguish them. Mag. 3, 7, and 11; A white, B pale blue, C red; A-B, distance= ii".5, p. = 142°; A-C, distance = 49", p. = 103°; R. A. V h. 30.5 m.; D.— 5° 59'. Just to the west (or right, as observer faces south) of Iota (^ is a smaller star, a pretty double, also not marked in our charts because of the danger of overcrowding. It is listed here, however, because it is so easy and pretty as to be noted by almost any observer of the region round the great nebula. The technical name for the star is Struve 747. It is a good object for a 2-inch telescope or even for a lox field-glass. Mag. 4.7 and 5.6; distance = 36"; p. = 223°; R. A.Vh. 30.1 m.;D.-6°5'. 299. — Sigma (ff) is one of the most remarkable of the multiple stars, a quintuple, three of its components being visible in a 3-inch, or even in a 2-inch, telescope. Mag. 3.9, 5, 9.5, 6.8, 6.3. A-B, distance = o".3, p. = 330°; AB-C,; distance = 1 1".3, p. = 237°; AB-D, distance = I2".8,p. = 83°; AB-E, distance = 41 ".4, p. = 61°; Hn ©bserver's Catalogue 131 E-D, distance = 30". I, p. = 231°; R. A. V h. 33-7 m.; D.-2° 39'. 300.— Lambda (A), the star that marks Orion's head, is a triple ; two of its components visible in a 3-mch. Mag. 3.7, 5.6, and 10; A yellow, B purplish; A-B, distance = 4".5, p. =43°; A-C, distance = 28".6, p. = 183°; R. A. V h. 29.6 m. ; D. + 9° 52'. 301.— Peg'-a-sus, the Winged Horse. (Maps pp. 61, 41, 55, 43. N. H., R. A. XXII h. 50 m.; D. + 20°.) A large constellation, of marked general interest because of the "great square" for which it is conspicuous. This is formed by its stars Alpha (a) or Markab, Beta (A) or Scheat, Gamma (y) or Algenib, and the Alpha (a) of Andromeda. But it has few objects for telescopic study. When the head of Medusa was struck off by Perseus, Pegasus — the Winged Horse — sprang from the blood of the Gorgon. Pegasus was afterward caught by Bellerophon with the golden bridle, gift of Athena. The hero then, after his triumph over the Chimjera, attempted to ascend to the heavens on his winged horse. He fell to the earth; but Pegasus, ascending, was given a place in the stars. For the con- nection (?) of Pegasus with Perseus and An- dromeda, see [i]. But this connection belongs to a much later legend. 302. — Epsilon (e) is a wide double star. Mag. 2.5 and 8.5; A yellow, B violet; distance= 138"; p. =323°; R. A. XXI h. 39.3 m.; D.+9° 25'. Arabic name, Enif. 303. — The cluster marked M 15 is globular in form, looking somewhat like a nebulous oval in a small telescope; but revealing its star- Istructure in larger instruments. R. A. XXI h. 25.1 m.; D.-l-ii° 44'. 304. — The little star Pi (tt) has near it another marked in some atlases as tt^. The pair make a pretty object for a 2-inch, or for a field-glass. The stars are of mags. 4.4 and 5.7; R. A. XXII h. 5.5m.;D.+ 32°4i'. 305-— Per'-se-us. (Maps pp. 59, 55> 43. 47- N. H., R. A. Ill h. 20 m.; D.+45°.) A rich and brilliant constellation of the northern sky, somewhat irregular in form, lying between Auriga and Cassiopeia. The breast of the hero is supposed to be at Alpha (a), the head at Gamma (/), one hand grasping his sword at the cluster h-X, and the other holding the head of Medusa at Beta (/3). One knee is at Mu (yu), the other at Xi (5). For the story of Perseus, see [i], in connection with Andromeda. 306. — The star Alpha (a) lies directly within the Milky Way and is the centre of a brilliant field of stars. There are few finer spectacles, whether for the opera-glass, the field-glass, or the small telescope. R. ,A. Ill h. 17.2 m.; D. -1-49° 30'. Arabic name*, Algenib or Marfak. 307. — Beta (/5) is the famous variable, Algol, discussed on p. 14. R. A. Ill h. 1.7 m. ; D.+40° 34'- 308. — The star Eta (7) is a double for a 3-inch. Mag. 3.9 and 8.5; A orange, B blue; distance = 28"; p. =300°; R. A. II h. 43.4 m.; D. + 55° 29'. 309. — The double star-cluster h-X is one of the very finest in the sky, and is peculiarly beautiful in small instruments. The use of high magnifying powers will necessarily reduce the size of the field and the impressiveness of the spectacle. On a 3-inch the best eyepiece to use is one from 25X to 40X; on a 2-inch telescope, use 15X to 25X. On telescopes of other apertures use powers proportionately low. See the illustration, p. 5. R. A. II h. i4m.;D.-f56°40'. 310. — Zeta (Q is a quadruple star; though a small instrument will show only two of the components. It is not easy for any telescope smaller than a 3J. Mag. 3, 9.3, 10, and 11; A white, B and C blue. A-B, distance = 12". 8 ; p. = 207°; R. A. Ill h. 47.8 m.; D. + 3i° 35'. 311. — A fine star-cluster marked M 34, a good object for a 2-inch or 3-inch telescope, lies on a line from Gamma (y) in Andromeda to Beta (ft) in Perseus. R. A. II h. 36 m.; D.+42° 21.' 320. — Pis'-ces, the Fishes. (Maps pp. 61, 41, N. H., R. A. o h. 30 m.; D.-fi5°.) A large constellation, lying in the track of the planets, between Aquarius and Aries. It is import- ant because of its position, but it has few brilliant objects of telescopic interest. 321. — ^Alpha («) is a fine double, but the com- ponents are so near each other as to be a little difficult with a 3-inch, and the distance seems to be decreasing. It is worth trying with a 3-inch, however; and a little experience, with good atmospheric conditions, will bring success. Mag. 4.3 and 5.2 ; A pale green, B blue; distance = 2".5; p. = 320°; R. A. I h. 56.9 m.; B.+ 2° 17'. Arabic name. El Rischa. 322. — Zeta (Q is an easy and pretty double star lying between Mu (m) and Epsilon ('=). Mag. 5.6 and 6.5; A white, B grayish; distance = 24"; p. =64°; R. A. I h. 8.5 m.; D. + 7° 3'. 323. — Psi ('/'); marked tp'' in some atlases; an easy double. Mag. 5.6 and 5.8; both white; distance = 3o"; p. = 160°; R. A. I h. 0.4 m.; D.-f 20° 56'. 330. — Pis'-cis Aus-tri'-nus, the Southern Fish. (Map p. 61. N. H., R. A. XXII h. 15 m.; D. — 30°.) Not to be confused with Pisces, the Fishes; see above. A southern constellation chiefly characterized by the fine first-magni- tude star Fo'-mal-haut (Fo'-mal-o), which is supposed to mark the Fish's mouth. It lies south of Aquarius, and is a conspicuous object in the southern sky during the er^.r^ evenings of autumn. a Beainner's Star^Bool? 331. — Fo'-mal-haut (pronounced Fo'-mal-o), to which reference has just been made, has a distant companion; dif. in R. A. 4.8 sec; p. = 195°; mag. of the two components 1.3 and 9.5. Many astronomers would rightly contend that stars so far apart should not be classified as a true double. But Smyth does well to list it because of the general interest in all first- magnitude stars. The dull blue companion is by no means easy. R. A. XXII h. 52.1 m.; D. —30° 9'. Distance of Fomalhaut is 24 light- years ; proper motion, o".37. In general type, it resembles Sirius [66]. 332. — Beta (/j) is an interesting double star, even in a 2-inch instrument. Mag. 4.4 and 7.8; distance = 30" ; p. = 172°; R. A. XXII h. 25.9 m.; D.-32° 52'. 333. — Gamma (y) is a double also but not so easy as the preceding. Mag. 4.5 and 8.8; distance = 4"; p. =270°; R. A. XXII h. 47 m.; D.-33°24'. Plei'-a-des, see [382]. Po-lar'-is, see [406]. Pol'-lux, see [187]. Pr*'-se-pe, see [52]. Pro'-cy-on, see [71]. Pup'-pis; Pyx'-is, see [25]. Reg'-u-lus, see [226]. Ri'-gel, see [292]. 335. — Sa-git'-ta; the Arrow. (Maps pp. 57, 61, 51; N. H., R. A. XIX h. 40 m.; D.-f i8°.) A small constellation lying in the Milky Way slightly to the north of Altair. It is of interest to the eye because it really looks like an arrow. Between Delta (t5) and Gamma (7), and slightly below a line connecting them, there lies a small cluster marked in some atlases M 71 and in others 4520, or 6838. It is not, impressive in a small instrument. R. A. XIX h. 49.3 m. ; D. + i8°3i'- 340. — Sa-git-ta'-rius, the Archer. (Maps pp. 57, 53, 61; N. H., R. A. XIX h. 15 m.; D. —25°.) A large constellation, in the track of the planets, between Capricornus and Scorpius. The constellation is not rich in double stars, but it presents a fine spectacle to the unaided eye and it lies in a region crowded with nebulas and star-clusters of great beauty. 341. — The object marked M 8 is, under good atmospheric conditions, visible to the naked eye. It can be found by projecting a line from the star Phi (cp) to Lambda (A.) and con- tinuing it an equal distance. The cluster is just below the termination of the line. It is a cluster superposed upon a fine nebula. See, however, the illustration on p. 115. R. A. XVII h. 57.7 m.; D.-24° 22'. 342. — Just north of the preceding object and more nearly at the termination of the line just suggested is the rich nebula marked M 20. It is sometimes called the "Trifid" nebula, because of its triple form. R. A. XVII h. 56.3 m.; D.-23°2'. 343. — The cluster M 22 lies on a line drawn from Tau (t) to Sigma (ff), continued about half as far again. It is a beautiful and impres- sive object. R. A. XVIII h. 30.3 m.; D. -23° 58'. 344. — This, marked M 17, is the famous Omega nebula, thus called by reason of its supposed resemblance to that Greek letter. It is ir- regular in form; a fine object. R. A. XVIII h. 14.9 m.; D. — 16° 13'. 345. — This cluster, M' 24, is not far from the above, a little to the north or just over it and, to the left — as we face southward. R. .A. XVIII h. 13 m.; D.-i8°28'. 346. — The multiple star Mu (yw), omitted from the Night Chart in order to avoid over-crowd- ing, is indicated in N. H. It is a fourth- magnitude star lying almost midway between M 8 and M 24, a little nearer the latter. While the star is a quintuple, a 3-inch instrument will probably show but two of the components to the average eye. M"ag. 3.5 and 9.5; distance = 48".3; p. =312°; R. A. XVIII h. 7.8 m.; D.-2i°5'. 350. — Scorp'-i-us, the Scorpion. (Maps pp. 53, 57; N. H., R. A. XVI h. 35 m.; 0.-30°.) The name of the group is sometimes ^written Scorpio. It is a large and important constel- lation lying in the track of the planets, between Libra and Sagittarius. It presents an impres- sive field of stars, beautifully grouped and bearing much likeness to the object for which it has been named. Indeed it looks more like the real scorpion of the tropics than do some of the weird illustrations of it presented in our mythological star-maps. 351. — Alpha (a), or Ant-a'-res, is one of the finest of the first-magnitude stars, somewhat varying in hue, but predominantly red. Hence its name Antares, opposed to, or rivalling. Mars, — Mars being of course the red planet. It was also called Kapdia 2xop7iiov by the Greeks, Cor Scorpionis by the Latins, and Kalb-al- 'akrab, by the Arabs, — all meaning the Scor- pion's Heart. It possesses a small companion star, but the components are not easily sepa- rable except in a telescope of 3|-inches or over. Some observers claim to have seen the small star with a 3-inch , under fine atmospheric conditions, but the average eye will require a larger instrument. Mag. 1.2 and 7; A red, B blue; distance = 3"; p. = 275°; R. A. XVI h. 23.3 m. ; D. —26° 13'. It is also a spectroscopic binary; p. 117, col. 2. Its distance is over a hundred light-years, but it is drawing nearer Missing Page Missing Page Missing Page Missing Page HALLEY'S COMET, MAY 26, 1910 From a photograph taken at the Lick Observatory 1,37 1D1I1I1I. Star 2)i0tance0, Star fIDotions, noagnitu&es, etc. We have seen, p. 9, that the stars are at such vast distances from us that the unit of measurement is the "light-year," — the distance traversed by light, at a velocity of over 186,320 miles a second, in a year of time. To find the distance of a star, the astronomer must determine its parallax — the angle subtended at the star by the radius of the earth's orbit. Although this base line represents the distance between Earth and Sun, or approxi- mately 93,000,000 miles, there are multitudes of stars which show no parallax. Indeed they are so remote that a line representing the whole diameter of the orbit, or over 185,000,- 000 miles, assumes but the aspect of a vanishing point in the perspective of the star's dis- tance. Bessel, a great German astronomer, obtained (1838) the first satisfactory measure of a parallax, — that of the small star known as 61, in Cygnus. It was long thought to be the nearest visible to the unaided eye from our latitudes, but this position now belongs to Sirius. A telescopic star, "Lalande 21,185," is the nearest known in the northern skies. In the following table the parallax of the stars is indicated in the column marked P. These parallaxes have been obtained by different astronomers, but they are here presented from the list of Kapteyn and Weersma, Groningen, 19 10; Kapteyn being the most generally accepted living authority on the general problem of stellar distances. They are not all entitled to equal weight. I have, therefore, ranked them in the col. marked F according to the degree of finality which should probably be accorded them. For these estimates of finality K. and W. are not responsible. A parallax classed as A is probably accurate within o".02; a parallax classed as B is probably accurate within o".03 or o".04; and C, within o".o5 or o."o6. In the column marked D is noted the distance of the star in light- years, based on the parallax given. The greater the distance, the more uncertain become all the conditions involved, so that the figures for stars at a light-distance exceeding 100 years become necessarily more like approximations than like rigid calctilations. In many cases, however, these approximations are as likely to be underestimates as overestimates. Where a negative parallax is indicated (by the minus sign preceding) the star is too far distant to be measured at all, and the light-distance can only be roughly stated as over 500 years. At the foot of the table are the figures for a few stars invisible to the naked eye. The velocity of "the runaway star," Groombridge 1830 (a faint star in Ursa Major), is over 200 miles a second, or over 720,000 miles an hour. No explanation of such phe- nomena is yet at hand. Most of the stars show traces of association into groups, different groups betraying a common drift. We now know that the stars, instead of being really "fixed," have motions of their own, relative to our own position in space. The motions of a star may be defined, in the terms of its annual displacement on the celestial sphere, in seconds of arc. This is usually called its proper motion, see the column marked P. M. Or when expressed as a velocity in miles per second it has been called the star's "Cross Motion. " This is indicated in the column marked C. M. To secure the velocity per minute multiply of course by 60. But the stars have another motion also^ — a motion that represents no displacement on the celestial sphere, for it is in the line of sight. This linear motion is indicated in the terms of velocity in miles per second in the column R. V. ( = radial velocity). When the star is 138 Distances anb \DeIocities 139 approaching our system, decreasing the distance at the velocity indicated, the minus sign accompanies the figure ; where the star is receding from us and the distance is increasing, the indicated velocity is preceded by the sign plus (+)■ Stars enclosed in brackets [ ] are visible only from extreme southern latitudes. Table A. Star Distances and Star Motions The Star [Alpha (a) of Centaurus] Sirius = Alpha (a) of Canis Major Tau (t) of Cetus Procy on = Alpha (a) of Canis Minor 61 of Cygnus Altair = Alpha (a) of Aquila Eta (t)) of Cassiopeia Xi (?) of Ursa Major. '. Omicron (o^) of Eridanus Zeta (X) of Hercules Mira = Omicron (o) of Cetus Fomalhaut = Alpha (a) of Piscis Austrinus Denebola = Beta (P) of Leo Beta (P) of Virgo Mu (|i) of Cassiopeia Gamma (7) of Draco Mu ((I) of Hercules Gamma (y) of Cygnus Vega = Alpha (o) of Lyra Theta (6) of Ursa Major Arc turus = Alpha (a) of Bootes Beta (P) of Cassiopeia Ras Alhague = Alpha (a) of Ophiuchus Aldebaran = Alpha (o) of Taurus Capella = Alpha (a) of Auriga Pollux = Beta (P) of Gemini Gamma (7) of Virgo [Alpha (a) of Crux] [Achemar = Alpha (a) of Eridanus] Polaris = Alpha (a) of Ursa Minor [Beta (P) of Centaurus] Regulus = Alpha (a) of Leo Mizar = Zeta (1) of Ursa Major Betelgeuze = Alpha (a) of Orion Antares = Alpha (a) of Scorpius Castor = Alpha (a^) of Gemini [Beta (P) of Crux] Alamak = Gamma (7) of Andromeda Rigel =Beta (P) of Orion [Canopus = Alpha (o) of Carina (Argo Navis)]. . Bellatrix = Gamma (7) of Orion Deneb = Alpha (a) of Cygnus Spica = Alpha (a) of Virgo Albireo = Beta (P) o f Cygnus Lalande 21, 185 (R- A. Xh. 57.9m.; D.+36° 38') Groombridge 34 (R- A- Oh. 12.5m.; D. +43° 27') Lalande 21,258 (R. A. Xlh. 0.5m. ; D. +44° 2') . Groombridge 1830 (R. A.XIh.47.2m.; D.+38° 26') P. 759 376 334 324 311 238 201 179 174 142 142 138 129 118 112 107 106 106 094 092 075 074 074 073 066 064 058 055 051 047 037 033 033 030 029 028 008 007 007 007 003 004 012 021 403 281 .203 D. 4-3 8.7 9.8 lO.I 10.5 137 16.2 18.2 18.8 22.9 22.9 23.6 25-3 27.6 29.1 30-5 30.8 30.8 34-7 35-5 43-5 44.1 44.1 44-7 49-4 50.9 56.2 59-3 64.0 69.4 88.1 99 99 109 112 116 408 466 466 466 500+ 500+ 500+ 500+ 8.1 11.6 I6.-I 32.0 A A B B A B B C B B B B C C B C 'C C B C A B B B B B B B B B B B A B B B B B B B A A A A A A B P.M. 3".66 l".32 i"-93 l".25 5"-25 •65 I ".25 •73 4".o8 .61 •23 •37 •51 •79 3".75 .025 .813 .003 •35 i".09 ?".28 •56 .26 .20 •44 .62 •55 .06 .09 .04 .04 •25 •13 •03 •03 .20 .06 .07 .00 .02 .02 .004 ■05 .01 4^77 2.85 4.46 7.07 CM 14.2 10.3 17.0 "•3 49.6 8.0 18.2 12.0 69.0 12.6 4^7 7^9 11.6 19.6 98.2 0.7 22.5 0.08 10.9 34^8 89^3 22.2 10.3 8.0 19.6 28.4 27.8 3^2 5^2 2^5 3^2 22.2 "•5 2.9 3^0 20.9 22.0 29.4 o. 8.4 34^9 29.8 64.8 204.3 140 a Beoinuer's Star*»Book A list is here given of the seventy brightest stars, indicating their magnitudes according to the Revised Harvard Photometry (1908) in the column marked H; and according to the determinations of the Astrophysical Observatory, Potsdam, in the column marked P, as shown in the Sternverzeichnis of Ambronn, 1907. In both H and P the figure is here Table B. Star Magnitudes Star Eirius= Alpha (a) of Canis Major [Canopus = Alpha (a) of Ca rina] [Alpha (a) of Centaurus].. . . Vega = Alpha (a) of Lyra. . . . Capella = Alpha (a) of Au riga Arcturus = Alpha (a) of Bo otes Rigel =Beta (P) of Orion Procyon = Alpha (o) of Ca- nis Minor [Achernar= Alpha (a) of Eridanus] [Beta (P) of Centaurus] Altair = Alpha (a) of Aquila. Betelgeuze = Alpha (a) of Orion, max [Alpha (a) of Crux] Aldebaran = Alpha (a) of Taurus Pollux = Beta (P) of Gemini Spica= Alpha (a) of Virgo., Antares = Alpha (a) of Scor- pius FomaIhaut = Alpha (a) of Piscis Austrinus Deneb= Alpha (a) of Cyg- nus Regulus = Alpha (a) of Leo, [Beta (P) of Crux] Castor = Alpha (a) of Gem- ini [Gamma (7) of Crux] Epsilon (e) of Canis Major. Alioth = Epsilon (e) of Ursa Major Bellatrix = Gamma (7) of Orion Lefath = Lambda (X) of Scorpius [Epsilon («) of Carina] Alnilam = Ep3ilon (e) of Or- ion Nath = Beta (P) of Taurus. . . [Beta (P) of Carina] [Alpha (a) of Triangulum Australe] Algenib= Alpha (a) of Per- seus Benetnasch = Eta {i\) of Ursa Major II —1.6 —0.9 o.i o.i 0.2 0.2 0-3 0-5 0.6 0.9 0.9 0.9 I.I I.I 1.2 1.2 1-3 1-3 1-3 1-5 1.6 1.6 1.6 1-7 1-7 1-7 1-7 1.8 1.8 1.8 1-9 1.9 1.9 0.4 0-5 0-3 0.8 1.2 1-5 1.6 1.8 2.2 2-3 10.76 5-75 2.29 2.29 2.09 2.09 1.91 1-59 1.44 1. 10 1. 10 1. 10 0.91 0.91 0.83 0.83 0.83 0.76 0.76 0.76 0.63 0.58 0.58 0.58 0.52 0.52 0.52 0.52 0.48 0.48 0.48 0.44 0.44 0.44 No. 35 36 37 38 39 40 41 42 43 44 45 46 47 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 star Zeta (J) of Orion Alhena = Gamma (y) of Gemini Dubhe = Alpha (a) of Ursa Major Epsilon («) of Sagittarius.. Wezen = Delta (S) of Canis Major Beta (P) of Canis Major. . . [Delta (8) of Vela] Theta (6) of Scorpius Menkalinan = Beta (P) of Auriga Polaris = Alpha (a) of Ursa Minor [Alpha (a) of Pavo] Ras Alhague = Alpha (o) of Ophiuchus Sigma (o-) of Sagittarius Algol = Beta (P) of Perseus, max Alpheratz= Alpha (a) of An- dromeda [Alpha (a) of Grus] Alphard = Alpha (a) of Hy- dra Mizar = Zeta {I) of Ursa Major Saiph = Kappa (k) of Orion. Alamak = Gamma (7) of An- dromeda [Lambda (X) of Vela] [Gamma (7) of Vela] Denebola = Beta (P) of Leo. . Hamal= Alpha (o) of Aries. . Deneb Kaitos = Beta (P) of Cetus Kochab = Beta (P) of Ursa Minor [Beta (P) of Grus] Alpha (o) of Cassiopeia, max. [Iota (i) of Carina] Gamma (7) of Cassiopeia. . . [Theta (0) of Centaurus] [Zeta (?) of Puppis] Gemma = Alpha (o) of Co- rona Borealis Gamma (7) of Cygnus Epsilon («) of Scorpius Mirach = Beta (p) of An- dromeda H 2.4 1-9 0.44 1-9 2-3 0.44 2.0 2.0 0.40 2.0 0.40 2.0 0.40 2.0 0.40 2.0 0.40 2.0 0.40 2.1 2.2 0.36 2.1 2-3 0.36 2.1 0.36 2.1 2-5 0.36 2.1 0.36 2.1 2-3 0.36 2.2 2-4 0.33 2.2 0-33 2.2 2.2 0-33 2.2 2.4 0-33 2.2 0.33 2.2 2.4 0.33 2.2 0-33 2.2 0.33 2.2 2.6 0.33 2.2 2.2 0-33 2.2 0-33 2.2 2.3 0-33 2.2 0.33 2.2 2.3 0-33 2-3 0.30 2.3 2.5 0.30 2-3 0.30 2-3 0.30 2.3 2.6 0.30 2-3 2-5 0.30 2.4 0.28 2-3 IRelative Brilliant 141 carried to only one decimal, fractions over .05 counting as .1. For example, the precise mag; of Sirius is —1.58. Stars south of the celestial equator were not included in the Potsdam determinations. In the column marked B is indicated the relative brilliancy of a number of the stars on a simple decimal scale, assuming Aldebaran — the Alpha (a) of Taurus — as approximately a first-magnitude star. No star is precisely of mag. 1.0. By this method it may be seen at a glance that Sirius is more than 10 times as bright as a standard first-magnitude, that Capella is more than twice as bright as such a star, and that Epsilon (f) in Ursa Major, the third star from the tip in the Dipper's handle, is about half as bright. These decimal notations are based on the magnitudes as shown in column H. The system of notation just described is far simpler than the comparison of stars by "magnitudes," for in the scale of magnitudes the beginner is confused by the occurrence of zero magnitudes and negative ( = minus) magnitudes, these notations applying to some of the brightest and most interesting stars. A 2d-magnitude star is about 2.51 times fainter than a first-magnitude, a 3d-mag. star is about 2.51 times fainter than a 2d-magnitude, etc. The scale, even in this direction, is confusing, because the brilliancy of the star does not increase with the increase of the numeral of magnitude, but the reverse. Yet in the other direction the conventional scale becomes still more troublesome, for as Aldebaran and Altair are approximately of the first magnitude, there is no way to indicate stars brighter than these, except by resorting to decimals of unity. We have been forced, therefore, to describe Vega as mag. o.i, Arcturus as mag. 0.2, and Sirius as lower in magnitude than zero, or of mag. minus, — 1.6. And this is the brightest star in the sky! Among the techni- calities of a really noble science this system is, in the judgment of the plain man, one of the "puzzles" of astronomy. As current text-books and monographs all assume the traditional photometric scale, the maps, etc., of this book have been composed in accordance with it. The beginner will find that the slight variations between the Harvard and Pots- dam results are chiefly due to the factor of color in the Hght of the stars. The Harvard results are usually accepted as standard in England and the United States. The first twenty of the seventy stars in the column marked H are generally classified as of the "first magni- tude" ; the remaining fifty, with some ten others, are of the " second magnitude. " We have seen that the individual stars are often designated by the Greek letter, used with the Latin genitive of the constellation name; see p. 12, second footnote. For readers who do not know Latin, some of these genitive forms that are less easily recognized are here given in italics:— Aries, Arietis; Cancer, Cancri; Cetus, Cetl; Cygnus, Cygni; Draco, Dra- conis; Gemini, Geminorum; Leo, Leonis; Lepus, Leporis; Libra, Librae fOrion, Orionis; Per- seus, Persei; Serpens, Serpentis; Taurus, Tauri; Ursa Major, Ursae Majoris; Virgo, Virginis. Some Variable Stars Many of the stars show marked changes in brilliancy, varying in magnitude. These variations are in many cases periodic, and in some instances we have been able to ascertain the causes of change ; see p. 13. In other cases no adequate explanation of these changes in brightness has been found. A few. of the best known are given in this list. Those marked S. B. are also spectroscopic binaries, their periods of variation corresponding to their periods of revolution. This may indicate that at minimum one component (as the stars revolve round their common centre of gravity) passes behind the other and is totally or -nartially eclipsed. The magnitude of each variable star at its maximum and at its minimum is indicated in the table below; and, in the column marked P, is indicated the 142 H Beainncr's Star^Booh period of variability in Days. The smaller variables are usually given, for symbols, the Arabic capitals in the order of their discovery in each constellation, — as R Leporis. For this use of the Latin genitive, see p. 141 ; also see second footnote on p. 12. Table C. Some Well-Known Variables Star Eta (ti) of Aquila (S. B.) [Eta (n) of Argo (Carina)] Epsilon («) of Auriga (S. B.). . . Alpha (a) of Cassiopeia Delta (S) of Cepheus (S. E.). . . Mu (|i) of Cepheus Mira = Omicron (o) of Cetus. . . Chi (x) of Cygnus Eta (ti) of Gemini (S. B.) Zeta (£) of Gemini (S. B.) Max. Min. ■7 4 7 ■4 4 .2 2 •7 4 .? 5 •7 9 13 .2 4 •7 4 7.18 9905. 5-37 331-6 406. 231-4 10.15 Star Ras Algethi= Alpha (a) of Hercules R of Lepus Delta (8) of Libra (S. B.) Iota (i) of Libra Sheliak = Beta ((3) of Lyra (vS. B.) Betelgeuze = Alpha (a) of Orion Algol = Beta ((3) of Perseus (S. B.) 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