File:Astronomy for high schools and colleges (1881) (14577186809).jpg

Identifier: astronomyforhigh00newc (find matches)
Title: Astronomy for high schools and colleges
Year: 1881 (1880s)
Authors: Newcomb, Simon, 1835-1909 Holden, Edward Singleton, 1846-1914, joint author
Subjects: Astronomy
Publisher: New York, H. Holt and Company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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sphere, as was first pointed out by An-drew Wilson of Glasgow. When a spot is seen at theedge of the disk, it appears as a notch in the limb, and iselliptical in shape. As the rotation carries it further andfurther on to the disk, it becomes more and more nearlycircular in shape, and after passing the centre of the diskthe appearances take place in reverse order. These observations were explained by Wilson, and more fully bySir William Herschel, by supposing the sun to consist of an in-terior dark cool mass, surrounded by two layers of clouds. The SOLAR SPOTS. 1391 outer layer, which forms the visible photosphere, was supposedextremely brilliant. The inner layer, which could not be seenexcept when a cavity existed in the photosphere, was supposedto be dark. The appearance of the edges of a spot, which hasbeen described as the penumbra, was supposed to arise fromthose dark clouds. The spots themselves are, according to thisview, nothing but openings through both of the atmospheres, the
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Fig. 80.—apparent path of solar spot at different seasons. nucleus of the spot being simply the black surface of the innersphere of the sun itself. This theory, which the figure on the next page exemplifies,accounts for the facts as they were known to Herschel. But whenit is confronted with the questions of the cause of the suns heatand of the method by which this heat has been maintained con-stant in amount for centuries, it breaks down completely. The 292 ASTRONOMY. conclusions of Wilson and Herschel, that the spots are depressionsin the suns surface, are undoubted. But the existence of a cool cen-tral and solid nucleus to the sun is now known to be impossible.The apparently black centres of the spots are so mostly by contrast.If they were seen against a perfectly black background, they wouldappear very bright, as has been proved by the photometric measuresof Professor Langley. And a cool solid nucleus beneath such anatmosphere as Herschel supposed would soon become gaseous bythe

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