SCHLESINGER, FRANK

SCHLESINGER, FRANK (1871–1943), U.S. astronomer and pioneer in stellar photography. Born in New York, Schlesinger obtained his doctorate with a thesis on a new type of measurement of a star cluster. He then began to develop his original methods for the determination of stellar parallaxes by means of celestial photography, revolutionizing the subject. In 1905 he was appointed director of the Allegheny Observatory, where he worked on the orbits of spectroscopic binary stars, devising simple methods of reducing spectrograms, and designing a new, sensitive measuring machine. In 1914 he started his ambitious plan of a large-scale parallax program. Within six years the first 365 star distances were determined, parallaxes with an average probable error of less than one hundredth of a second of arc. In 1920 he became director of the Yale University Observatory, and in 1925 he set up a South African station at Johannesburg with a 26-inch telescope of 36 feet focal length. The importance of these "trigonometric parallaxes" lies in the fact that they are the basis of the present distance scale of the universe. With their help, all spectroscopic and other distance determinations are eventually calibrated. In 1940 Schlesinger published his first "Bright Star Catalogue," giving all the essential data for all stars brighter than 6.5 visual magnitude. He did outstanding work on stellar proper motions and star positions obtained with wide-angle cameras, and a long series of these "Zone Catalogues" was published in the Yale Observatory Transactions. Schlesinger was a leading figure in the formation of the International Astronomical Union. He was its president from 1932 to 1935, and many other academic honors were awarded to him. -BIBLIOGRAPHY: Bibliographical Memoirs of the National Academy of Science, 24 (1947), 105–44; Spencer Jones, in: Monthly Notices of the Royal Astronomical Society, 104 (1944), 94–98. (Arthur Beer)