An Introduction to Astronomy

Forest Ray Moulton

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• Publié par: adde
• Publié le: 08 décembre 2010
• Nombre de lectures: 32
• Langue: English
• Poids de l'ouvrage: 13 Mo

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Project Gutenberg’s An Introduction to Astronomy, by Forest Ray Moulton This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org Title: An Introduction to Astronomy Author: Forest Ray Moulton Release Date: April 24, 2010 [EBook #32000] Language: English Character set encoding: ISO-8859-1 *** START OF THIS PROJECT GUTENBERG EBOOK AN INTRODUCTION TO ASTRONOMY *** Produced by Brenda Lewis, Andrew D. Hwang, Bup, and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.) transcriber’s note Figures may have been moved with respect to the surrounding text. Minor presentational changes have been made without comment. A Typographical corrections are documented in the L TEX source file. The spelling “Leverrier” has been retained from the original. This PDF file is formatted for screen viewing, but may be easily formatted for printing. Please consult the preamble of the A L TEX source file for instructions. AN INTRODUCTION TO ASTRONOMY NEW YORK · BOSTON · CHICAGO · DALLAS ATLANTA · SAN FRANCISCO LONDON · BOMBAY · CALCUTTA MELBOURNE THE MACMILLAN COMPANY MACMILLAN & CO., Limited THE MACMILLAN CO. OF CANADA, Ltd. TORONTO Fig. 1. — The Lick Observatory, Mount Hamilton, California. AN INTRODUCTION TO ASTRONOMY BY FOREST RAY MOULTON, Ph.D. PROFESSOR OF ASTRONOMY IN THE UNIVERSITY OF CHICAGO RESEARCH ASSOCIATE OF THE CARNEGIE INSTITUTION OF WASHINGTON NEW AND REVISED EDITION New York THE MACMILLAN COMPANY 1916 All rights reserved Copyright, 1906 and 1916, By THE MACMILLAN COMPANY. Set up and electrotyped. Published April, 1906. Reprinted November, 1907; July, 1908; April, 1910; April, 1911; September, 1912; September, 1913: October, 1914. New and revised edition November, 1916. Norwood Pre& J. S. Cushing Co. — Berwick & Smith Co. Norwood, Mass., U.S.A. PREFACE The necessity for a new edition of “An Introduction to Astronomy” has furnished an opportunity for entirely rewriting it. As in the first edition, the aim has been to present the great subject of astronomy so that it can be easily comprehended even by a person who has not had extensive scientific training. It has been assumed that the reader has no intention of becoming an astronomer, but that he has an interest in the wonderful universe which surrounds him, and that he has arrived at such a stage of intellectual development that he demands the reasons for whatever conclusions he is asked to accept. The first two of these assumptions have largely determined the subject matter which is presented; the third has strongly influenced the method of presenting it. While the aims have not changed materially since the first edition was written, the details of the attempt to accomplish them have undergone many, and in some cases important, modifications. For example, the work on reference points and lines has been deferred to Chapter iv. If one is to know the sky, and not simply know about it, a knowledge of the coördinate systems is indispensable, but they always present some difficulties when they are encountered at the beginning of the subject. It is believed that the present treatment prepares so thoroughly for their study and leads so naturally to them that their mastery will not be found difficult. The chapter on telescopes has been regretfully omitted because it was not necessary for understanding the remainder of the work, and because the space it occupied was needed for treating more vital parts of the subject. The numerous discoveries in the sidereal universe during the last ten years have made it necessary greatly to enlarge the last chapter. As now arranged, the first chapters are devoted to a discussion of the earth and its motions. They present splendid examples of the characteristics and methods of science, and amply illustrate the care with which scientific theories are established. The conclusions which are set forth are bound up with the development of science from the dawn of recorded history to the recent experiments on the rigidity and the elasticity of the earth. They show how closely various sciences are interlocked, and how much an understanding of the earth depends upon its relations to the sky. They lead naturally to a more formal treatment of the celestial sphere and a study of the constellations. A familiarity with the brighter stars and the more conspicuous constellations is revi PREFACE vii garded as important. One who has become thoroughly acquainted with them will always experience a thrill when he looks up at night into a cloudless sky. The chapter on the sun has been postponed until after the treatment of the moon, planets, and comets. The reason is that the discussion of the sun necessitates the introduction of many new and difficult topics, such as the conservation of energy, the disintegration of radioactive elements, and the principles of spectrum analysis. Then follows the evolution of the solar system. In this chapter new and more serious demands are made on the reasoning powers and the imagination. Its study in a measure develops a point of view and prepares the way for the consideration, in the last chapter, of the transcendental and absorbingly interesting problems respecting the organization and evolution of the sidereal universe. Lists of problems have been given at the ends of the principal divisions of the chapters. They cannot be correctly answered without a real comprehension of the principles which they involve, and in very many cases, especially in the later chapters, they lead to important supplementary results. It is strongly recommended that they be given careful consideration. The author is indebted to Mr. Albert Barnett for the new star maps and the many drawings with which the book is illustrated, with the exception of Figs. 23 and 30, which were kindly furnished by Mr. George Otis. He is indebted to Professor David Eugene Smith for photographs of Newton, Kepler, Herschel, Adams, and Leverrier. He is indebted to the Lick, Lowell, Solar, and Yerkes observatories for a large amount of illustrative material which was very generously furnished. He is under deeper obligations to his colleague, Professor W. D. MacMillan, than this brief acknowledgment can express for assistance on the manuscript, on the proofs, and in preparing the many problems which appear in the book. F. R. MOULTON. The University of Chicago, September 25, 1916. CONTENTS CHAPTER I Preliminary Considerations ARTS. PAGE 1. 2. 3. 4. 5. 6. 7. 8. Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 The value of science . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 The origin of science . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 The methods of science . . . . . . . . . . . . . . . . . . . . . . . . . . 5 The imperfections of science . . . . . . . . . . . . . . . . . . . . . . 8 Great contributions of astronomy to science . . . . . . . . . . . . 11 The present value of astronomy . . . . . . . . . . . . . . . . . . . . 12 The scope of astronomy . . . . . . . . . . . . . . . . . . . . . . . . . 14 CHAPTER II THE EARTH I. The Shape of the Earth 9. 10, 12, 13. 16. 17. 18. Astronomical problems respecting the earth . . . . . . . . . . . . 20 11. Proofs of the earth’s sphericity . . . . . . . . . . . . . . . 21, 24 14, 15. Proofs of the earth’s oblateness . . . . . . . . . . . . . 24–28 Size and shape of the earth . . . . . . . . . . . . . . . . . . . . . . 26 The theoretical shape of the earth . . . . . . . . . . . . . . . . . . 29 Different kinds of latitude . . . . . . . . . . . . . . . . . . . . . . . 31 Historical sketch on the shape of the earth . . . . . . . . . . . . . 31 II. The Mass of the Earth and the Condition of its Interior 19. The principle by which mass is determined . . . . . . . . . . . . 34 20. The mass and density of the earth . . . . . . . . . . . . . . . . . . 35 21–23. Methods of determining the density of the earth . . . . 36–39 24. Temperature and pressure in the earth’s interior . . . . . . . . . 40 25, 26. Proofs of the earth’s rigidity and elasticity . . . . . . . . 41, 47 27. Historical sketch on the mass and rigidity of the earth . . . . . 49 viii