Chapter I: Front Matter

_An Active Prominence of the Sun, 140,000 Miles High,
photographed July 9, 1917._]

ASTRONOMY

THE SCIENCE OF THE HEAVENLY BODIES

BY

DAVID TODD

DIRECTOR EMERITUS, AMHERST COLLEGE OBSERVATORY

NEW YORK AND LONDON
HARPER & BROTHERS
PUBLISHERS MCMXXII

Copyright 1922

BY P. F. COLLIER & SON COMPANY

Sir William Rowan Hamilton, the eminent mathematician of Dublin, has, of all writers ancient and modern, most fittingly characterized the ideal science of astronomy as man's golden chain connecting the heavens to the earth, by which we "learn the language and interpret the oracles of the universe."

The oldest of the sciences, astronomy is also the broadest in its relations to human knowledge and the interests of mankind. Many are the cognate sciences upon which the noble structure of astronomy has been erected: foremost of all, geometry and the higher mathematics, which tell us of motions, magnitudes and distances; physics and chemistry, of the origin, nature, and destinies of planets, sun, and star; meteorology, of the circulation of their atmospheres; geology, of the structure of the moon's surface; mineralogy, of the constitution of meteorites; while, if we attack, even elementally, the fascinating, though perhaps forever unsolvable, problem of life in other worlds, the astronomer must invoke all the resources that his fellow biologists and their many-sided science can afford him.

The progress of astronomy from age to age has been far from uniform--rather by leaps and bounds: from the earliest epoch when man's planet earth was the center about which the stupendous cosmos wheeled, for whom it was created, and for whose edification it was maintained--down to the modern age whose discoveries have ascertained that even our stellar universe, the vast region of the solar domain, is but one of the thousands of island universes that tenant the inconceivable immensities of space.

Such results have been attainable only through the successful construction and operation of monster telescopes that bring to the eye and visualize on photographic plates the faintest of celestial objects which were the despair of astronomers only a few years ago.

But the end is not yet; astronomy to-day is but passing from infancy to youth. And with new and greater telescopes, with new photographic processes of higher sensitivity, with the help of modern invention in overcoming the obstacle of the air--that constant foe of the astronomer--who will presume to set down any limit to the leaps and bounds of astronomy in the future?

So rapid, indeed, has been the progress of astronomy in very recent years that the present is especially favorable for setting forth its salient features; and this book is an attempt to present the wide range of astronomy in readable fashion, as if a story with a definite plot, from its origin with the shepherds of ancient Chaldea down to present-day ascertainment of the actual scale of the universe, and definite measures of the huge volume of supersolar giants among the stars.

DAVID TODD
AMHERST COLLEGE OBSERVATORY
November, 1921

CONTENTS

CHAPTER PAGE

I. ASTRONOMY A LIVING SCIENCE 9

II. THE FIRST ASTRONOMERS 19

III. PYRAMID, TOMB, AND TEMPLE 23

IV. ORIGIN OF GREEK ASTRONOMY 27

V. MEASURING THE EARTH--ERATOSTHENES 30

VI. PTOLEMY AND HIS GREAT BOOK 33

VII. ASTRONOMY OF THE MIDDLE AGES 37

VIII. COPERNICUS AND THE NEW ERA 42

IX. TYCHO, THE GREAT OBSERVER 45

X. KEPLER, THE GREAT CALCULATOR 49

XI. GALILEO, THE GREAT EXPERIMENTER 53

XII. AFTER THE GREAT MASTERS 57

XIII. NEWTON AND MOTION 62

XIV. NEWTON AND GRAVITATION 66

XV. AFTER NEWTON 73

XVI. HALLEY AND HIS COMET 83

XVII. BRADLEY AND ABERRATION 90

XVIII. THE TELESCOPE 93

XIX. REFLECTORS--MIRROR TELESCOPES 102

XX. THE STORY OF THE SPECTROSCOPE 111

XXI. THE STORY OF ASTRONOMICAL PHOTOGRAPHY 125

XXII. MOUNTAIN OBSERVATORIES 139

XXIII. THE PROGRAM OF A GREAT OBSERVATORY 152

XXIV. OUR SOLAR SYSTEM 162

XXV. THE SUN AND OBSERVING IT 165

XXVI. SUN SPOTS AND PROMINENCES 174

XXVII. THE INNER PLANETS 189

XXVIII. THE MOON AND HER SURFACE 193

XXIX. ECLIPSES OF THE MOON 206

XXX. TOTAL ECLIPSES OF THE SUN 209

XXXI. THE SOLAR CORONA 219

XXXII. THE RUDDY PLANET 227

XXXIII. THE CANALS OF MARS 235

XXXIV. LIFE IN OTHER WORLDS 242

XXXV. THE LITTLE PLANETS 254

XXXVI. THE GIANT PLANET 260

XXXVII. THE RINGED PLANET 264

XXXVIII. THE FARTHEST PLANETS 267

XXXIX. THE TRANS-NEPTUNIAN PLANET 270

XL. COMETS--THE HAIRY STARS 273

XLI. WHERE DO COMETS COME FROM? 279

XLII. METEORS AND SHOOTING STARS 283

XLIII. METEORITES 290

XLIV. THE UNIVERSE OF STARS 294

XLV. STAR CHARTS AND CATALOGUES 300

XLVI. THE SUN'S MOTION TOWARD LYRA 304

XLVII. STARS AND THEIR SPECTRAL TYPE 307

XLVIII. STAR DISTANCES 311

XLIX. THE NEAREST STARS 319

L. ACTUAL DIMENSIONS OF THE STARS 321

LI. THE VARIABLE STARS 324

LII. THE NOVAE, OR NEW STARS 331

LIII. THE DOUBLE STARS 334

LIV. THE STAR CLUSTERS 336

LV. MOVING CLUSTERS 341

LVI. THE TWO STAR STREAMS 345

LVII. THE GALAXY OR MILKY WAY 350

LVIII. STAR CLOUDS AND NEBULAE 357

LIX. THE SPIRAL NEBULAE 361

LX. COSMOGONY 366

LXI. COSMOGONY IN TRANSITION 380

LIST OF ILLUSTRATIONS

ACTIVE PROMINENCE OF THE SUN, 140,000 MILES HIGH _Frontispiece_
FACING PAGE
NICHOLAS COPERNICUS 64

GALILEO GALILEI 64

JOHANN KEPLER 65

SIR ISAAC NEWTON 65

THE HUNDRED-INCH REFLECTING TELESCOPE AT MOUNT WILSON 96

THE FORTY-INCH REFRACTING TELESCOPE, YERKES OBSERVATORY 96

150-FOOT TOWER, MOUNT WILSON, A DIAGRAM OF TOWER AND PIT 97

150-FOOT TOWER--EXTERIOR VIEW 97

VIEW LOOKING DOWN INTO THE PIT BENEATH 150-FOOT TOWER 97

MOUNT WILSON SOLAR OBSERVATORY--THE 100-FOOT DOME 128

MOUNT CHIMBORAZO, THE BEST SITE IN THE WORLD FOR
AN OBSERVATORY 128

LICK OBSERVATORY, MOUNT HAMILTON, CALIFORNIA 129

PHOTOGRAPHING WITH THE 40-INCH REFRACTOR 129

GREAT SUNSPOT GROUP OF AUGUST 8, 1917 160

CALCIUM FLOCCULI ON THE SUN 161

ECLIPSE OF THE MOON, WITH THE LUNAR SURFACE VISIBLE 161

MOON'S SURFACE IN THE REGION OF COPERNICUS 192

SOUTH CENTRAL PORTION OF THE MOON, AT LAST QUARTER 193

CORONA OF THE SUN DURING AN ECLIPSE 224

VENUS, IN THE CRESCENT PHASE 225

MARS, SHOWING BRIGHT POLAR CAP 225

JUPITER, THE GIANT PLANET 256

NEPTUNE AND ITS SATELLITES 256

SATURN, WITH EDGE OF RINGS ONLY IN VIEW 257

SATURN, WITH RINGS DISPLAYED TO FULLEST EXTENT 257

TWO VIEWS OF HALLEY'S COMET 288

SWIFT'S COMET, WHICH SHOWED REMARKABLE TRANSFORMATIONS 288

METEOR TRAIL IN FIELD WITH FINE NEBULAE 289

RING NEBULA IN LYRA 320

DUMB-BELL NEBULA 321

STAR CLOUDS AND BLACK HOLES IN SAGITTARIUS 352

GREAT NEBULA IN ANDROMEDA 353