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National Geographic : 1925 Jan
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THE NATIONAL GEOGRAPHIC MAGAZINE Photograph from Mt. Wilson Observatory THE THREE GREAT TYPES OF SPECTRA THROUGH WHICH THE STARS TELL THEIR STORIES When light comes into a spectroscope from a solid body glowing with white heat, it presents the ordinary prismatic colors of the rainbow. When the light comes from glowing gas, instead of from a solid, it gives a black band crossed by bright lines as shown in the middle band of the picture. But when it comes from a solid glowing body and passes through a cooler gas, like the atmosphere of the sun, it gives a prismatic band, but crossed by dark lines, as in the lower part of the picture (see text, page 1o6). of a given star may be held on a definite spot on the plate, building up its image to a perceivable magnitude. On the plate the flying minute is fixed forever, and at will the bit of sky it covers may be revived, although generations may have passed since the photograph was taken. Appreciating the value of a vast direc tory of the stars which would show their relative positions on given dates, eighteen great observatories in all parts of the world undertook to make such a directory of all stars down to the eleventh magni tude. The record has been finished and contains some six million stars. Imagine the inestimable value of these plates a thousand years from now, if they can be made to endure. Compared with similar plates taken then, they would re veal the changes in the celestial map in ten centuries. Nothing could serve better to clear up the mysteries of the universe than such a comparison. Yerkes and other observatories feel that there should be established an ade quate depot where these vastly important records can be stored under conditions that will protect them against the men aces of fire, tornado, earthquakes, and other cataclysms for a thousand years, and are looking for the far-visioned man who, by endowing their care, would trans mit these invaluable records to the people living a millennium hence. THE STORIES THE CENTURIES WILL TELL Nordmann, after speaking of some of the marvelous things that the studies of the stars have revealed, says that all these results are nothing in comparison with those which the generations that come after us will discover, as from century to century they rephotograph these stars and compare their plates with ours. 114
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