Popular Astronomy

POPULAR ASTRONOMY. BY SIMON NBWCOMB, LL. IX, PROFESSOR, U. S. NAVAL OBSERVATORY. WITH ONE HUNDRED AND TWELVE ENGRAVINGS, AND FIVE MAPS OF THE STARS. HP n b a n MACMILLAN AND CO. 1878. THE GREAT TELESCOPE OF THE UNITED STATES NAVAL OBSERVA TORY, WASHINGTON. CONSTRUCTED BY ALVAN CLAIIK AND SONS, 1873. PREFACE. To prevent a possible misapprehension in scientific quar ters, the author desires it understood that the present work is not designed either to instruct the professional investi gator or to train the special student of astronomy. Its main object is to present the general reading public with a con densed view of the history, methods, and results of astro nomical research, especially in those fields which are of most popular and philosophic interest at the present day, couched in such language as to be intelligible without mathematical study. He hopes that the earlier chapters will, for the most part, be readily understood by any one having clear geomet rical ideas, and that the later ones will be intelligible to all. To diminish the difficulty which the reader may encounter from the unavoidable occasional use of technical terms, a Glossary has been added, including, it is believed, all that are used in the present work, as well as a number of others which may be met with elsewhere. Respecting the general scope of the work, it may be said that the historic and philosophic sides of the subject have been treated with greater fulness than is usual in works of this character, while the purely technical side has been pro portionately condensed. Of the four parts into which it is divided, the first two treat of the methods by which the mo vi PREFACE. tions and the mutual relations of the heavenly bodies have been investigated, and of the results of such investigation, while in the last two the individual peculiarities of those bodies are considered in greater detail. The subject of the general structure and probable development of the universe, which, in strictness, might be considered as belonging to the first part, is, of necessity, treated last of all, because it re quires all the light that can be thrown upon it from every available source. Matter admitting of presentation in tabular form has, for the most part, been collected in the Appendix, where will be found a number of brief articles for the use of both the general reader and the amateur astronomer. The author has to acknowledge the honor done him by several eminent astronomers in making his work more com plete and interesting by their contributions. Owing to the great interest which now attaches to the question of the con stitution of the sun, and the rapidity with which our knowl edge in this direction is advancing, it was deemed desirable to present the latest views of the most distinguished investi gators of this subject from their own pens. Four of these gentlemen Rev. Father Secchi, of Rome M. Faye, of Paris Professor Young, of Dartmouth College and Professor Lang ley, of Allegheny Observatory have, at the authors request, presented brief expositions of their theories, which will be found in their own language in the chapter on the sun. An Addendum gives the basis of the remarkable modifi cation of the theory of the solar spectrum proposed by Dr. Henry Draper, which appeared while the sheets were passing through the press. CONTENTS. PART I. THE SYSTEM OF THE WORLD HISTORICALLY DEVELOPED. PAGIt INTRODUCTION 1 CHAPTER I. THE ANCIENT ASTRONOMY, OR THE APPARENT MOTIONS OF THE HEAV ENLY BODIES 7 1. The Celestial Sphere 7 2. The Diurnal Motion 9 3. Motion of the Sun among the Stars 13 4. Precession of the Equinoxes. The Solar Year 19 5. The Moons Motion 21 6. Eclipses of the Sun and Moon 24 7. The Ptolemaic System 32 8. The Calendar 44 CHAPTER II. THE COPERNICAN SYSTEM, OR THE TRUE MOTIONS OF THE HEAVENLY BODIES 51 1. Copernicus 51 2. Obliquity of the Ecliptic Seasons, etc. on the Copernican Sys tem 61 3. Tycho Brahe 66 4. Kepler. His Laws of Planetary Motion 68 5...