Identifier: adolfostahllectu00astruoft (find matches)
Title: The Adolfo Stahl lectures in astronomy, delivered in San Francisco, California, in 1916-17 and 1917-18, under the auspices of the Astronomical Society of the Pacific
Year: 1919 (1910s)
Authors: Astronomical Society of the Pacific Aitken, Robert Grant, 1864-1951
Subjects: Astronomy
Publisher: San Francisco Stanford University Press
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: MSN

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of anysingle comet, but we do know that cometary masses are ex-ceedingly small in comparison with the masses of the smallestplanets. The recent comets which have approached close toMars, Earth, Mercury, or Venus have produced no appreciabledisturbances in the motions of those planets. We have described the known members of the solar systemas to dimensions, masses, orbits and geometrical relations oneto another. We have seen that they form the Suns system—asystem very completely isolated in space, and independent ofother systems so far as its internal relations are concerned. Nowthe solar system as a whole is traveling through space withreference to the other members of the stellar system. SirWilliam Herschel suggested, a century and a third ago, thatthe apparent motions of the other stars were such as toindicate a motion of our star and its system toward the con-stellation Hercules, and this conclusion has been amply verifiedby Herschels successors. The logic of the demonstration is
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H The Solar System 11 very simple. Let us use an illustration which every one hashad or may have the opportunity to test. Suppose the observeris traveling rapidly by railway train across a level tract ofcountry, say toward the west. He will notice that the trees,buildings, or other objects on his western horizon appear toseparate gradually. Similar observations on the trees andother objects on the eastern horizon will show that they appearto approach each other. The trees and buildings on the horizonto the right and to the left of him will seem to be travelingtoward the east. The explanation is apparent. The motion ofthe solar system through space is a much more complicatedproblem, in that we must deal with space of three dimensions,instead of the two dimensions of the terrestrial surface, and thestellar objects which the observer sees in all directions from himare themselves in motion. However, if the positions of a greatnumber of stars have been accurately determined at some pastepo

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