Preface
How many thousands of educated people, trained in the best schools, or even graduates of the great universities, have made the confession: “I never got a grip on astronomy in my student days. They didn’t make it either plain or interesting to me; and now I am sorry for it.”
The purpose of the writer of this book is to supply the need of such persons, either in school, or at home, after school-days are ended. He does not address himself to special students of the subject—although they, too, may find the book useful at the beginning—but to that vast, intelligent public for whom astronomy is, more or less, a “mystical midland,” from which, occasionally, fascinating news comes to their ears. The ordinary text-book is too overladen with technical details, and too summary in its treatment of the general subject, to catch and hold the attention of those who have no special preliminary interest in astronomy. The aim here is to tell all that really needs to be told, and no more, and to put it as perspicuously, compactly, and interestingly, as possible. For that reason the book is called a “nutshell.”
The author has been sparing in the use of diagrams, because he believes that, in many cases, they have been over-pressed. There is a tendency to try to represent everything to the eye. This is well to a certain extent, but there is danger that by pursuing this method too far the power of mental comprehension will be weakened. After all, it is only by an intelligent use of the imagination that progress can be made in such a science as astronomy. The reader is urged to make a serious effort to understand what is said in the text, and to picture it in his mind’s eye, before referring to the diagrams. After he has thus presented the subject to his imagination, he may refer to the illustrations, and correct with their aid any misapprehension. For this reason the cuts, with their descriptions, have been made independent of the regular text, although they are placed in their proper connections throughout the book.
G. P. S.
April, 1912.
Part I — The Celestial Sphere
PAGES
Definition of Astronomy—Fundamental Law of the Stars—Relations of the Earth to the Universe—Ordinary Appearance of the Sky—The Horizon, the Zenith, and the Meridian—Locating the Stars—Altitude and Azimuth—Circular or Angular Measure—Altitude Circles and Vertical Circles—The Apparent Motion of the Heavens—The North Star and Phenomena Connected with it—Revolution of the Stars round the Pole—Locating the Stars on the Celestial Sphere—Astronomical Equivalents of Latitude and Longitude—Parallels of Declination and Hour Circles—“The Greenwich of the Sky”—Effects Produced by Changing the Observer’s Place on the Earth—The Parallel Sphere, the Right Sphere, and the Oblique Sphere—The Astronomical Clock—The Ecliptic—Apparent Annual Revolution of the Sun round the Earth—Inclination of the Ecliptic to the Equator: its Cause and its Effects—The Equinoxes—Importance of the Vernal Equinox—The Equinoctial Colure—The Solstices—Poles of the Ecliptic—Celestial Latitude and Longitude—The Zodiac—The Precession of the Equinoxes: its Cause and Effects—Revolution of the Celestial Poles—Past and Future Pole Stars 3-64
Part II — The Earth
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| Nature, Shape, and Size of the Earth—The Polar Compression and Equatorial Protuberance, and their Cause—The Attraction of Gravitation—The Mass of the Earth: how Found—How the Earth Holds the Moon, and the Sun the Planets—The Tides—How the Moon and Sun Produce Tides—Spring Tides and Neap Tides—The Atmosphere—The Law and Effects of Refraction—Dip of the Horizon—The Aberration of Light—Time: how Measured—Sidereal, Apparent Solar, and Mean Solar Time—The Clock and the Sun—Day and Night—Where the Days Begin—The Seasons—Effects of the Varying Declination of the Sun—Polar and Equatorial Day and Night—The Tropics and the Polar Circles—Inequality of Length of the Seasons—When the Seasons in the Two Hemispheres will be Reversed—The Calendar, the Year, and the Month—Reformations of the Calendar—Different Measures of the Month | 67-123 |
Part III — The Solar System
PAGES
The Sun—Distance, Size, and Condition of the Sun—Temperature of the Sun—Solar Heat on the Earth, and its Mechanical Equivalent—Peculiar Rotation of the Sun—Sun-spots, their Appearance and Probable Cause—Faculæ—The Photosphere—Solar Prominences—Explosive Prominences—The Solar Corona—Parallax, and the Measure of Distances—Spectroscopic Analysis—How the Elements in the Sun Reveal their Presence—List of the Principal Solar Elements—The Moon—Origin of the Moon—Appearance of its Surface—Gravity on the Moon—The Phases of the Moon—Causes of the Absence of a Lunar Atmosphere—Eclipses—How the Moon Causes Eclipses of the Sun—The Laws Governing Eclipses—The Shadow during a Solar Eclipse—Eclipses of the Moon—Number of Eclipses in a Year—The Saros—The Planets—Kepler’s Laws of Planetary Motion—Mercury—Venus—Mars, and its So-called Canals—Theories about Mars—Jupiter, its Belts and its Satellites—The “Great Red Spot”—Saturn, its Rings and its Satellites—Composition of the Rings—Uranus and Neptune—Comets, and the Laws of their Motion—Composition of Comets—The Pressure of Light and its Connection with Comets’ Tails—Breaking up of Comets—Meteors and their Relations to Comets—The November Meteors and Other Celebrated Showers—Meteorites or Bolides which Fall upon the Earth—The Question of their Origin 127-215
Part IV — The Fixed Stars
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| Division of the Stars into Magnitudes—Division of the Stars according to their Spectra—Stars Larger and Smaller than the Sun—The Distances of the Stars—Variable Stars—Double and Binary Stars—Spectroscopic Binaries and how they are Discovered—Proper Motions of the Stars—Number of the Stars—New, or Temporary Stars—The Milky Way—The Nebulæ—The Two Kinds of Nebulæ—Spiral Nebulæ—The Nebular Hypothesis—Applications of Photography to Stars and Nebulæ—The Constellations—How to Learn the Constellations—Their Antiquity—Description of the Principal Constellations Visible from the Northern Hemisphere at Various Times of the Year | 219-257 |
Index 259