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