Stars of the Southern Skies

Part 1

Transcriber’s Notes:

Underscores “” before and after a word or phrase indicate italics_ in the original text. Small capitals have been converted to SOLID capitals. Illustrations and footnotes have been moved so they do not break up paragraphs. Typographical and punctuation errors have been silently corrected.

STARS OF THE SOUTHERN SKIES

STARS OF THE SOUTHERN SKIES

BY M. A. ORR (MRS. JOHN EVERSHED)

AUTHOR OF “AN EASY GUIDE TO SOUTHERN STARS” AND “DANTE AND THE EARLY ASTRONOMERS”

“All experience is an arch wherethrough We glimpse the untravelled world whose margin fades Forever and forever.”

WITH ILLUSTRATIONS

LONGMANS, GREEN AND CO. 39 PATERNOSTER ROW, LONDON FOURTH AVENUE & 30TH STREET, NEW YORK BOMBAY, CALCUTTA, AND MADRAS 1915

All rights reserved

TO MISS MARY PROCTOR

CONTENTS

CHAP. PAGE THE GREEK LETTERS x INTRODUCTION xi I. THE CONSTELLATIONS OF THE SOUTH: MODERN GROUPS 1 II. THE CONSTELLATIONS OF THE SOUTH: ANCIENT GROUPS 6 III. THE TEN BRIGHTEST STARS OF THE SOUTHERN HEMISPHERE 15 IV. STARS OF DIFFERENT AGES 23 V. SOME NEAR NEIGHBOURS 32 VI. DOUBLE AND MULTIPLE STARS 35 VII. THE ASTONISHING STAR, ETA ARGŪS 40 VIII. MIRA, THE WONDERFUL STAR 46 IX. ECLIPSING STARS 51 X. SHORT-PERIOD VARIABLE STARS 54 XI. IRREGULAR AND DOUBTFUL VARIABLES 57 XII. STAR-CLUSTERS 59 XIII. GLOBULAR STAR-CLUSTERS 66 XIV. NEBULAE 72 XV. OTHER TYPES OF NEBULAE 80 XVI. THE CLOUDS OF MAGELLAN 85 XVII. THE MILKY WAY 88

LIST OF ILLUSTRATIONS

PAGE MAP OF THE SOUTHERN HEMISPHERE to face Title

THE OLD CONSTELLATION FIGURES OF THE SOUTHERN HEMISPHERE to face page 6

THE ARCHER page 11 From a Babylonian Boundary Stone now in the British Museum

THE STAR-CLUSTER, 47 TOUCANI to face page 68 From Sir John Herschel’s drawing

THE MILKY WAY IN SCORPIO, LUPUS, AND ARA to face page 88 Photographed at Hanover, Cape Colony, by Bailey and Schultz

THE GREEK LETTERS

α Alpha ν Nu β Beta ξ Xi γ Gamma ο Omicron δ Delta π Pi ε Epsilon ρ Rho ζ Zeta σ Sigma η Eta τ Tau θ Theta υ Upsilon ι Iota φ Phi κ Kappa χ Chi λ Lambda ψ Psi μ Mu ω Omega

INTRODUCTION

This book is for those who have learned or are learning to recognise the southern constellations, but have not read much about astronomy, and have only an opera-glass or small telescope, or no instrument but their own eyes, for examining the stars. I assume that they have studied some simple guide to the constellations like Proctor’s, or my Southern Stars, and that they would like to know something more about the stars they are looking at—how far off they are, how large, if they remain always the same, and if there is any connection between the different parts of this immense universe of stars and nebulae.

I hope that the book will be useful to teachers and parents, helping them to answer some of the searching questions children put, and to teach some of the facts of astronomy in the most vivid and unforgettable way—viz. in connection with special stars and nebulae which are at the moment being admired. If an opera-glass or field-glass can be put into the children’s hands, so that they themselves can see a faint white spot turn into a lovely cluster of stars, it will give them a share in the thrill of discovery, and help them to understand what large telescopes can show.

A map of the southern hemisphere is here given for ready reference, but it would be well to possess a good atlas which gives the letters and numbers assigned to all bright stars and shows the positions of the brightest star-clusters and nebulae. Norton’s Star-Atlas and Telescopic Handbook is an excellent one, small enough to be handy, yet complete as far as it goes, and up to date, clear, and convenient to use.

Published at 5s. by Gall & Inglis, Edinburgh and London.

My intention is to treat specially of stars and nebulae visible in southern countries, so I have confined myself almost entirely to those of the southern hemisphere, though of course many which are north of the celestial equator can be seen also. My readers will find that the southern hemisphere possesses the most beautiful part of the Milky Way, the two brightest stars in the sky, the finest coloured star-cluster and the largest globular cluster, the brightest double star, the nearest of the stars, and the brightest of the large gaseous nebulae. Let us add that the southern hemisphere has been less studied than the north, and therefore there is an even wider field for amateur workers.

Stars of the Southern Skies

Part 2

THE CONSTELLATIONS OF THE SOUTH: MODERN GROUPS

When we speak of the southern constellations, everyone thinks of the Southern Cross, and every traveller coming south for the first time is eager to see it. Some are disappointed because it is small and irregular, but it is very brilliant, and lies in an extremely rich region of the Milky Way. Very beautiful, too, is the way in which it is seen rising on its side and gradually becoming upright as it reaches its greatest height above the horizon, then sloping again as it glides westward.

The Cross seems to have been first so named by the Spanish explorer Amerigo Vespucci, at the beginning of the sixteenth century, and it was also described in letters by the Florentine Andrea Corsali, who says it is so beautiful that in his opinion no other constellation in the sky is worthy to be compared with it. Some think, however, that the stars had already been recognised as forming a Cross as early as the thirteenth century, because Dante in his Purgatory speaks of four stars which glorified the southern sky; but he does not say they were in the form of a cross, and he tells us that they had never been seen before by mortal man except by our first parents, whose original dwelling-place he sets in the southern hemisphere. This negatives the suggestion that some traveller had described them to him.

About the same time as the Cross, other groups were named by sailors and travellers in the part of the sky round about the south pole, for this region had been left a blank by the framers of the ancient constellations, doubtless because they lived too far north to see it. Some students of astronomy in the Middle Ages concluded that there really were no stars in this part, and Ristoro of Arezzo gravely argued that this proved the absence of any land further south than India and Ethiopia; for where there are no stars to pour down influences on the earth no animals can live, and therefore no vegetation is needed for their food, and no land for it to grow on.

The new constellations were mostly named after strange birds and fishes seen by explorers in their southern voyages, and they were admitted to scientific astronomy by Bayer, who made a map of the skies in 1604. He also introduced the plan of naming each star in a constellation by a Greek letter, the brightest of each constellation usually being called Alpha, the next brightest Beta, and so on. One of these constellations is Grus, the Crane (originally called the Flamingo), and it is convenient to be familiar with it, because from it we may easily identify several others. The chief stars of Grus form a striking curve with a bright star close beside it. This bright star is Alpha Gruis, and the brightest in the curve is Beta. A line through Alpha and Beta leads in one direction to the brightest star of the Phoenix, in the other direction to the brightest of the Indian; a line through Alpha and the little naked-eye double Delta takes one to Pavo, the Peacock; a line through Gamma (at one end of the curve) and Alpha goes to the brightest star in the Toucan. And these are all the modern groups containing bright stars except the Southern Triangle, near the Pointers to the Cross (see p. 6), and Columba, the Dove, not far from Sirius, each of which has one star brighter than third magnitude. We may, however, also notice Alpha Hydri, the brightest star in the small Water-Snake, close to the bright star Achernar, and Alpha Doradūs, the brightest of the Sword-Fish, between Canopus and Achernar.

Stars are classified by astronomers in “magnitudes,” i.e. degrees of brightness, those of first magnitude being the brightest. Stars below sixth magnitude cannot be seen with the naked eye.

In the eighteenth century the French astronomer Lacaille, who did much excellent work in the southern hemisphere with a tiny telescope of only half an inch aperture, had the unhappy idea of filling up the spaces still left empty with scientific instruments. It is easy to make Birds of Paradise and Flying Fishes out of the stars, but such things as telescopes, easels, and sextants do not lend themselves to irregular groups, and they are very much out of place among the mythical beasts and heroes which we are accustomed to see on our star-maps. Fortunately the beginner need not learn to recognise these intruders, for there are no bright stars in them, although there are many interesting objects for telescopic study. We need only note that Octans, the Octant, occupies the region in which the south pole is situated, which is quite bare of bright stars. The pole itself may be found by drawing a line from head to foot of the Cross and carrying it on about four times as far again; or if the Cross is invisible, the pole may be found near the middle of a line from Canopus to Alpha Pavonis.

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