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ASTRONOMY OF TO-DAY
[Illustration: THE TOTAL ECLIPSE OF THE SUN OF AUGUST 30TH, 1905.
The Corona; from a water-colour sketch, made at Burgos, in Spain, during
the total phase, by the French Artist, Mdlle. ANDRÉE MOCH.]
ASTRONOMY OF
TO-DAY
_A POPULAR INTRODUCTION IN
NON-TECHNICAL LANGUAGE_
By
CECIL G. DOLMAGE, M.A., LL.D., D.C.L.
Fellow of the Royal Astronomical Society; Member of
the British Astronomical Association; Member of
the Astronomical Society of the Pacific; Membre
de la Société Astronomique de France;
Membre de la Société Belge
d'Astronomie
With a Frontispiece in Colour
and 45 Illustrations & Diagrams
_THIRD EDITION_
LONDON
SEELEY AND CO. LIMITED
38 GREAT RUSSELL STREET
1910
PREFACE
The object of this book is to give an account of the science of
Astronomy, as it is known at the present day, in a manner acceptable to
the _general reader_.
It is too often supposed that it is impossible to acquire any useful
knowledge of Astronomy without much laborious study, and without
adventuring into quite a new world of thought. The reasoning applied to
the study of the celestial orbs is, however, of no different order from
that which is employed in the affairs of everyday life. The science of
mathematics is perhaps responsible for the idea that some kind of
difference does exist; but mathematical processes are, in effect, no
more than ordinary logic in concentrated form, the _shorthand of
reasoning_, so to speak. I have attempted in the following pages to take
the main facts and theories of Astronomy out of those mathematical forms
which repel the general reader, and to present them in the _ordinary
language of our workaday world_.
The few diagrams introduced are altogether supplementary, and are not
connected with the text by any wearying cross-references. Each diagram
is complete in itself, being intended to serve as a pictorial aid, in
case the wording of the text should not have perfectly conveyed the
desired meaning. The full page illustrations are also described as
adequately as possible at the foot of each.
As to the coloured frontispiece, this must be placed in a category by
itself. It is the work of the _artist_ as distinct from the scientist.
The book itself contains incidentally a good deal of matter concerned
with the Astronomy of the past, the introduction of which has been found
necessary in order to make clearer the Astronomy of our time.
It would be quite impossible for me to enumerate here the many sources
from which information has been drawn. But I acknowledge my especial
indebtedness to Professor F.R. Moulton's _Introduction to Astronomy_
(Macmillan, 1906), to the works on Eclipses of the late Rev. S.J.
Johnson and of Mr. W.T. Lynn, and to the excellent _Journals of the
British Astronomical Association_. Further, for those grand questions
concerned with the Stellar Universe at large, I owe a very deep debt to
the writings of the famous American astronomer, Professor Simon Newcomb,
and of our own countryman, Mr. John Ellard Gore; to the latter of whom I
am under an additional obligation for much valuable information
privately rendered.
In my search for suitable illustrations, I have been greatly aided by
the kindly advice of Mr. W. H. Wesley, the Assistant Secretary of the
Royal Astronomical Society. To those who have been so good as to permit
me to reproduce pictures and photographs, I desire to record my best
thanks as follows:--To the French Artist, Mdlle. Andrée Moch; to the
Astronomer Royal; to Sir David Gill, K.C.B., LL.D., F.R.S.; to the
Council of the Royal Astronomical Society; to Professor E.B. Frost,
Director of the Yerkes Observatory; to M.P. Puiseux, of the Paris
Observatory; to Dr. Max Wolf, of Heidelberg; to Professor Percival
Lowell; to the Rev. Theodore E.R. Phillips, M.A., F.R.A.S.; to Mr. W.H.
Wesley; to the Warner and Swasey Co., of Cleveland, Ohio, U.S.A.; to the
publishers of _Knowledge_, and to Messrs. Sampson, Low & Co. For
permission to reproduce the beautiful photograph of the Spiral Nebula in
Canes Venatici (Plate XXII.), I am indebted to the distinguished
astronomer, the late Dr. W.E. Wilson, D.Sc., F.R.S., whose untimely
death, I regret to state, occurred in the early part of this year.
Finally, my best thanks are due to Mr. John Ellard Gore, F.R.A.S.,
M.R.I.A., to Mr. W.H. Wesley, and to Mr. John Butler Burke, M.A., of
Cambridge, for their kindness in reading the proof-sheets.
CECIL G. DOLMAGE.
LONDON, S.W.,
_August 4, 1908._
PREFATORY NOTE TO THE SECOND EDITION
The author of this book lived only long enough to hear of the favour
with which it had been received, and to make a few corrections in view
of the second edition which it has so soon reached.
_December 1908._
CONTENTS
CHAPTER I
PAGE
THE ANCIENT VIEW 17
CHAPTER II
THE MODERN VIEW 20
CHAPTER III
THE SOLAR SYSTEM 29
CHAPTER IV
CELESTIAL MECHANISM 38
CHAPTER V
CELESTIAL DISTANCES 46
CHAPTER VI
CELESTIAL MEASUREMENT 55
CHAPTER VII
ECLIPSES AND KINDRED PHENOMENA 61
CHAPTER VIII
FAMOUS ECLIPSES OF THE SUN 83
CHAPTER IX
FAMOUS ECLIPSES OF THE MOON 101
CHAPTER X
THE GROWTH OF OBSERVATION 105
CHAPTER XI
SPECTRUM ANALYSIS 121
CHAPTER XII
THE SUN 127
CHAPTER XIII
THE SUN--_continued_ 134
CHAPTER XIV
THE INFERIOR PLANETS 146
CHAPTER XV
THE EARTH 158
CHAPTER XVI
THE MOON 183
CHAPTER XVII
THE SUPERIOR PLANETS 209
CHAPTER XVIII
THE SUPERIOR PLANETS--_continued_ 229
CHAPTER XIX
COMETS 247
CHAPTER XX
REMARKABLE COMETS 259
CHAPTER XXI
METEORS OR SHOOTING STARS 266
CHAPTER XXII
THE STARS 278
CHAPTER XXIII
THE STARS--_continued_ 287
CHAPTER XXIV
SYSTEMS OF STARS 300
CHAPTER XXV
THE STELLAR UNIVERSE 319
CHAPTER XXVI
THE STELLAR UNIVERSE--_continued_ 329
CHAPTER XXVII
THE BEGINNING OF THINGS 333
CHAPTER XXVIII
THE END OF THINGS 342
INDEX 351
LIST OF ILLUSTRATIONS
LIST OF PLATES
PLATE
THE TOTAL ECLIPSE OF THE SUN
OF AUGUST 30, 1905 _Frontispiece_
I. THE TOTAL ECLIPSE OF THE SUN
OF MAY 17, 1882 _To face page_ 96
II. GREAT TELESCOPE OF HEVELIUS " " 110
III. A TUBELESS, OR "AERIAL" TELESCOPE " " 112
IV. THE GREAT YERKES TELESCOPE " " 118
V. THE SUN, SHOWING SEVERAL
GROUPS OF SPOTS " " 134
VI. PHOTOGRAPH OF A SUNSPOT " " 136
VII. FORMS OF THE SOLAR CORONA
AT THE EPOCHS OF SUNSPOT
MAXIMUM AND SUNSPOT
MINIMUM RESPECTIVELY.
(A) THE TOTAL ECLIPSE OF
THE SUN OF DECEMBER 22, 1870.
(B) THE TOTAL ECLIPSE OF
THE SUN OF MAY 28, 1900 " " 142
VIII. THE MOON _To face page_ 196
IX. MAP OF THE MOON, SHOWING
THE PRINCIPAL "CRATERS,"
MOUNTAIN RANGES AND
"SEAS" " " 198
X. ONE OF THE MOST INTERESTING
REGIONS ON THE MOON " " 200
XI. THE MOON (SHOWING SYSTEMS
OF "RAYS") " " 204
XII. A MAP OF THE PLANET MARS " " 216
XIII. MINOR PLANET TRAILS " " 226
XIV. THE PLANET JUPITER " " 230
XV. THE PLANET SATURN " " 236
XVI. EARLY REPRESENTATIONS OF
SATURN " " 242
XVII. DONATI'S COMET " " 256
XVIII. DANIEL'S COMET OF 1907 " " 258
XIX. THE SKY AROUND THE NORTH
POLE " " 292
XX. ORION AND HIS NEIGHBOURS " " 296
XXI. THE GREAT GLOBULAR CLUSTER
IN THE SOUTHERN CONSTELLATION
OF CENTAURUS " " 306
XXII. SPIRAL NEBULA IN THE CONSTELLATION
OF CANES VENATICI " " 314
XXIII. THE GREAT NEBULA IN THE
CONSTELLATION OF ANDROMEDA _To face page_ 316
XXIV. THE GREAT NEBULA IN THE
CONSTELLATION OF ORION " " 318
LIST OF DIAGRAMS
FIG. PAGE
1. THE PTOLEMAIC IDEA OF THE UNIVERSE 19
2. THE COPERNICAN THEORY OF THE SOLAR
SYSTEM 21
3. TOTAL AND PARTIAL ECLIPSES OF THE MOON 64
4. TOTAL AND PARTIAL ECLIPSES OF THE SUN 67
5. "BAILY'S BEADS" 70
6. MAP OF THE WORLD ON MERCATOR'S PROJECTION,
SHOWING A PORTION OF THE PROGRESS
OF THE TOTAL SOLAR ECLIPSE OF
AUGUST 30, 1905, ACROSS THE SURFACE
OF THE EARTH 81
7. THE "RING WITH WINGS" 87
8. THE VARIOUS TYPES OF TELESCOPE 113
9. THE SOLAR SPECTRUM 123
10. A SECTION THROUGH THE SUN, SHOWING HOW
THE PROMINENCES RISE FROM THE
CHROMOSPHERE 131
11. ORBIT AND PHASES OF AN INFERIOR PLANET 148
12. THE "BLACK DROP" 153
13. SUMMER AND WINTER 176
14. ORBIT AND PHASES OF THE MOON 184
15. THE ROTATION OF THE MOON ON HER AXIS 187
16. LAPLACE'S "PERENNIAL FULL MOON" 191
17. ILLUSTRATING THE AUTHOR'S EXPLANATION OF
THE APPARENT ENLARGEMENT OF CELESTIAL
OBJECTS 195
18. SHOWING HOW THE TAIL OF A COMET IS
DIRECTED AWAY FROM THE SUN 248
19. THE COMET OF 1066, AS REPRESENTED IN THE
BAYEUX TAPESTRY 263
20. PASSAGE OF THE EARTH THROUGH THE THICKEST
PORTION OF A METEOR SWARM 269
ASTRONOMY OF TO-DAY
CHAPTER I
THE ANCIENT VIEW
It is never safe, as we know, to judge by appearances, and this is
perhaps more true of astronomy than of anything else.
For instance, the idea which one would most naturally form of the earth
and heaven is that the solid earth on which we live and move extends to
a great distance in every direction, and that the heaven is an immense
dome upon the inner surface of which the stars are fixed. Such must
needs have been the idea of the universe held by men in the earliest
times. In their view the earth was of paramount importance. The sun and
moon were mere lamps for the day and for the night; and these, if not
gods themselves, were at any rate under the charge of special deities,
whose task it was to guide their motions across the vaulted sky.
Little by little, however, this simple estimate of nature began to be
overturned. Difficult problems agitated the human mind. On what, for
instance, did the solid earth rest, and what prevented the vaulted
heaven from falling in upon men and crushing them out of existence?
Fantastic myths sprang from the vain attempts to solve these riddles.
The Hindoos, for example, imagined the earth as supported by four
elephants which stood upon the back of a gigantic tortoise, which, in
its turn, floated on the surface of an elemental ocean. The early
Western civilisations conceived the fable of the Titan Atlas, who, as a
punishment for revolt against the Olympian gods, was condemned to hold
up the expanse of sky for ever and ever.
Later on glimmerings of the true light began to break in upon men. The
Greek philosophers, who busied themselves much with such matters,
gradually became convinced that the earth was spherical in shape, that
is to say, round like a ball. In this opinion we now know that they were
right; but in their other important belief, viz. that the earth was
placed at the centre of all things, they were indeed very far from the
truth.
By the second century of the Christian era, the ideas of the early
philosophers had become hardened into a definite theory, which, though
it appears very incorrect to us to-day, nevertheless demands exceptional
notice from the fact that it was everywhere accepted as the true
explanation until so late as some four centuries ago. This theory of the
universe is known by the name of the Ptolemaic System, because it was
first set forth in definite terms by one of the most famous of the
astronomers of antiquity, Claudius Ptolemæus Pelusinensis (100-170
A.D.), better known as Ptolemy of Alexandria.
In his system the Earth occupied the centre; while around it circled in
order outwards the Moon, the planets Mercury and Venus, the Sun, and
then the planets Mars, Jupiter, and Saturn. Beyond these again revolved
the background of the heaven, upon which it was believed that the stars
were fixed--
"Stellis ardentibus aptum,"
as Virgil puts it (see Fig. 1).
[Illustration: FIG. 1.--The Ptolemaic idea of the Universe.]
The Ptolemaic system persisted unshaken for about fourteen hundred years
after the death of its author. Clearly men were flattered by the notion
that their earth was the most important body in nature, that it stood
still at the centre of the universe, and was the pivot upon which all
things revolved.