iHpil Wd'- !)'..!X;W!iw<il.;! a6 8a. Cornell IDlnivetslt^ OF THE IRew IPorh State CoUeae of agriculture .,%,..x..i:'±e .ii£>\.kho Date Due Library Bureau Cat. No. 1137 Cornell University Library QB 51.B2 Star-land; being talks with young people 3 1924 002 961 187 Cornell University Library The original of tliis bool< is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31 924002961 1 87 STAE-LAND BEING TALKS WITH YOUNG PEOPLE ABOUT THE WONDERS OF THE HEAVENS SIR ROBERT STAWELL BALL, F.R.S. LOWKDEAN PROFESSOR OF ASTEONOMi' IN THE UNIVERSITY OF CAMBRIDGE AUTHOR OF "THE STORY OF THE HEAVENS," ETC. •ffUustrateb NEW AND REVISED EDITION Boston, U.S.A., and London , : ^j GINN & COMPANY, PUBLISHEES die %t\t;mwta. IJreeti 1899 (5155 ,2.z-y-c^ Enteeed at Statiokers' Hall COPYKIGHT, 1899, BY CASSELL & COMPANY, LIMITED ALL EIGHTS KESEKVED (Co THOSE YOUNG FRIENDS WHO HAVE ATTENDED MY CHRISTMAS LECTURES THIS LITTLE BOOK IS DEDICATED PREFACE TO FIRST EDITION. It has long been the custom at the Royal Institu- tion of Great Britain to provide each Christmastide a course of Lectures specially addressed to a juvenile audience. On two occasions, namely, in 1881 and in 1887, the Managers entrusted this honorable duty to me. The second course was in the main a repetition of the first ; and on my notes and recollections of both the present little volume has been founded. I am indebted to my friends Rev. Maxwell Close, Mr. Akthue Rambaut, and Dr. John Todhunter for their kindness in reading the proofs. ROBERT S. BALL. Obseevatort, Co. Dublin, Oct. 22, 1889. CONTENTS. LECTURE I. THE SUN. PAGE The Heat and Brightness of the Sun — Farther Benefits that we receive from the Sun — The Distance of the Sun — How As- tronomers measure the Distances of the Heavenly Bodies — Tlie Apparent Smallness of Distant Objects — The Shape and Size of the Sun — Tlie Spots on the Sun — Appearances seen during a Total Eclipse of the Sun — Night and Day — The Daily Rotation of the Earth — The Annual Motion of the Earth round the Sun — The Changes of the Seasons — Sun- shine at the North Pole 1 LECTURE II. THE MOON. The Phases of our Attendant the Moon — The Size of the Moon — How Eclipses are produced — Effect of the Moon's Distance on its Appearance — A Talk about Telescopes — How the Telescope aids us in Viewing the Moon — Tele- scopic Views of the Lunar Scenery — On the Origin of the Lunar Craters — The Movements of the Moon — On the Pos- sibility of Life in the Moon .... .74 LECTURE IIL THE INNER PLANETS. Mercury, Venus, and Mars — How to make a Drawing of our System—The Planet Mercury— The Planet Venus — The Transit of Venus — Venus as a World — The Planet Mars vii VlU CONTENTS. PAGE and his Movements — The Ellipse — The Discoveries made by Tycho and Kepler — The Discoveries made by Newton — The Geography of Mars — The Satellites of Mars — How the Telescope aids in Viewing Faint Objects — The Asteroids, or Small Planets 134 LECTURE IV. THE GIAKT PLANETS. Jupiter, Saturn, Uranus, Neptune — Jupiter — The Satellites of Jupiter — Saturn — The Nature of the Rings — William Her- schel — The Discovery of Uranus — The Satellites of Uranus — The Discovery of Neptune 212 LECTURE V. COMETS AND SHOOTING STARS. The Movements of a Comet — Encke's Comet — The Great Comet of Halley — How the Telegraph is used for Comets — The Parabola — The Materials of a Comet — Meteors — What be- comes of the Shooting Stars — Grand Meteors — The Great November Showers — Other Great Showers — Meteorites 255 LECTURE VL STARS. We try to make a Map — The Stars are Suns — The Numbers of the Stars — The Clusters of Stars — The Rank of the Earth as a Globe in Space — The Distances of the Stars — The Brightness and Color of Stars — Double Stars — How we find what the Stars are made of — The Nebulfe — What the Neb- ulae are made of — Photographing the Nebulae — Conclusion 318 CONCLUDING CHAPTER. / / HOW TO NAME THE STARS. 381 STAR-LAND. LECTURE I. THE SUN. The Heat and Brightness oJ the Sun — Further Benefits that we receive from the Sun — The Distance of the Sun — How Astronomers measure the Distances of the Heavenly Bodies — The Apparent Smallness of Distant Objects — The Shape and Size of the Sun — The Spots on the Sun — Appearances seen during a Total Eclipse of the Sun — Night and Day — The Daily Rotation of the Earth — The Annual Motion of the Earth round the Sun — The Changes of the Seasons — Sunshine at the North Pole. THE HEAT AND BRIGHTNESS OF THE SUN. We can all feel that the sun is very hot, and we know that it is very big and a long way off. Let us first talk about the heat from the sun. On a cold day it is pleasant to go into a room with a good fire, and everybody knows that the nearer we go to the fire, the more strongly we feel the heat. The boy who is at the far end of the room may be shivering with cold, while those close to the fire are as hot as they find to be pleasant. If we could draw much nearer to the sun than we actually are, we should find the heat greatly increased. Indeed, if we went close enough, the tem- perature would rise so much that we could not endure it; we should be roasted. On the other hand, we 1 ; Z STAR-LAND. should certainly be frozen to death if we were trans- ported much further away from the sun than we are now. We are able to live comfortably, because our bodies are just arranged to suit the warmth which the sun sends to that distance from it at which the earth is actually placed. Suppose you were able to endure any degree of heat, and that you had some way of setting out on a voyage to the sun. Take with you a wax candle, a leaden bullet, a penny, a poker, and a flint. Soon after you have started you find the warmth from the sun increas- ing, and the candle begins to get soft and melt away. Still, on you go, and you notice that the leaden bullet gets hotter and hotter, until it becomes too hot to touch, until at last the lead has melted, as the wax had previously done. However, you are still a very long way from the sun, and you have the penny, the poker, and the flint remaining. As you approach closer to the luminary the heat is ever increasing, and at last you notice that the penny is beginning to get red-hot go still nearer, and it melts away, and follows the example of the bullet and the candle. If you still press onwards, you find that the iron poker, which was red-hot when the penny melted, begins to get brighter and brighter, till at last it is brilliantly white, and becomes so dazzling that you can hardly bear to look at it; then melting commences, and the poker is changed into liquid like the penny, the lead, and the wax. Yet a little nearer you may cany the flint, which is now glowing with the same fervor which fused the poker, but even the flint itself will have THE BURNING-GLASS. 3 to yield at last and become, not merely a liquid like water, but a vapor like steam. You will ask, how do we learn all this ? As nobody could ever make such a journey, how can we feel certain that the sun is so excessively hot ? I know that what Fig. 1. — How to use the Burning-glass. I say is true for various reasons, but I will only mention one, which is derived from an experiment with the burning-glass, that most boys have often tried. We may use one of those large lenses that are intended for magnifying photographs. But almost any kind of lens will do, except it be too flat, as those in spectacles generally are. On a fine sunny day in sum- mer, you turn the burning-glass to the sun, and by STAR-LAND. holding a piece of paper at the proper distance a bright spot will be obtained (Fig. 1). At that spot there is intense heat, by which a match can be lighted, gun- FiQ. 2. — The Noonday Gun. powder exploded, or the paper itself kindled. The broad lens collects together the rays from the sun that fall upon it, and concentrates them in one spot, which consequently becomes hot and bright. If we merely used a flat piece of glass the sunbeams would go THE NOONDAY GUN. 5 straight through ; they would not be gathered together, and they would not be strong enough to burn the paper. The lens, you see, is not flat ; its faces are curved, and they thus acquire the power of bending in rays of light or heat, so as to unite their effect on that one point which we call the focus. When a great number of rays Fig. 3. — a Tell-tale for the Sun. are thus collected on the same spot, each of them con- tributes a little warmth. Some ingenious person has turned this principle to an odd use, by arranging a burning-glass over a cannon in such a way that just when noon arrived the spot of light should reach the touch-hole of the cannon and fire it off.