AAS 205th Meeting, 9-13 January 2005
Session 4 HAD Poster Session II
Poster, Monday, January 10, 2005, 9:20am-6:30pm, Exhibit Hall

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[4.01] A. A. Michelson's Jovian Galilean-Satellite Interferometer at Lick Observatory in 1891

D. E. Osterbrock (UCO/Lick Obs., UCSC)

Albert A. Michelson, America's first Nobel laureate in physics, measured the angular diameter of the red supergiant star Betelgeuse in 1920 with Francis G. Pease, using the 100-inch Mount Wilson reflector as the basis of his stellar interferometer. But he had first published the concept in 1890 and tested it on celestial objects with a telescope at Lick Observatory in 1891. He used its 12-inch refractor to measure the angular diameters of the four Galilean satellites of Jupiter, assisted at the telescope by W. W. Campbell, then a young astronomer who had just joined the Lick staff. Edward S. Holden, the Lick director, had invited Michelson to come to Mount Hamilton and use its telescopes as a guest observer.

Michelson had first tried and proved his method on artificial circular disks in his laboratory at Clark University, Worcester, Mass., using a 2-inch "glass." Then in 1889 and 1890 he hoped to test it at Harvard College Observatory, but apparently the telescope or the atmospheric conditions did not work out. At Lick he did achieve success, and his measured angular diameters were nearer to the true values we know from close-up space measurements of today than those of any of the top visual observers of the time. Correspondence in the Lick Archives shows that Michelson intended to come back there to use its big 36-inch refractor to improve the measurements, but he never did so.

Selections from Michelson's published papers and photographs of him, the telescope, and the instrument will be posted.

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Bulletin of the American Astronomical Society, 36 5
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