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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youngest starsas well as the oldest are red and the blue-white stars occupy amiddle position. This is not the place to present the forcefularguments brought to the support of each of these hypotheses,or to discuss their relative merits. I have mentioned themmerely to point out that one of the greatest difficulties in theway of the acceptance of the two-branched evolutionary theoryis the close association of the helium stars with diffuse nebu-losity such as exists in the constellation of Orion and in thePleiades. There is no correlation whatever between suchnebulae and red stars. This is perhaps as good a place as any to insist upon thenecessity of discriminating between the facts of observationand the theories which may be based upon those facts.Though elementary, the distinction is frequently lost sight ofand astronomy, or rather the reputation of the astronomer,suffers. It is a fact that the companion star in the system ofEpsilon Hydrae changes its position continuously with respect
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PLATE XLIV. The Pleiades. From a photograph by Sir Isaac Roberts, Dec. 8, 1888, exposure 4 hours. News from the Stars 167 to the brighter star in such a manner that after 15 years itreturns to its apparent starting point. The theory is that the• change is due to the motion of the two bodies in elliptic orbitsabout a common center of gravity under the law of gravitation.In this case the evidence from numerous double stars is sooverwhelmingly strong that the theory has as much weight asthe observed facts. In other instances, as for example, theidentity in the quality of the light of star and nebula or thearrangement of stellar spectra, the facts are beyond questionbut they may perhaps be subject to more than one interpreta-tion. We are quite willing to abandon any theory, howevercherished, whenever the facts fail to support it. Let us again return to the constellation of Orion in orderto consider a photograph taken by Dr. Curtis with the Cross-ley reflector only a week ago (Plate XLV)

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