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A Fifty-foot Interferometer Telescope1


THE angular diameter of a star was measured for the first time by Mr. Francis G. Pease at the Mount Wilson Observatory on December 13, 1920, with a 20-foot Michelson interferometer attached to the 100-inch reflecting telescope. The method employed is due to Prof. Michelson, who had adjusted the interferometer and tested it on stars during the previous summer, with the assistance of Mr. Pease. Since that time Mr. Pease has measured the diameters of Betelgeuse, Arcturus, Aldebaran, and Antares. On the basis of the best available values of their parallaxes, the corresponding linear diameters are 215,000,000, 21,000,000, 270,000,000, and 400,000,000 miles respectively. These stars are all in the giant stage, with densities ranging from 0.000001 (Antares) to 0.0002 (Arcturus). The Sun, a dwarf star 866,000 miles in diameter, in a much more advanced state of development, has a density of 1.4 (water= 1).

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