SCHLESINGER, FRANK

born May 11, 1871, New York City died July 10, 1943, Lyme, Conn., U.S. American astronomer who pioneered in the use of photography to map stellar positions and to measure stellar parallaxes, from which the most direct determinations of distance can be made. From 1899 to 1903 Schlesinger was in charge of the International Latitude Observatory at Ukiah, Calif. He then was appointed astronomer at the Yerkes Observatory, Williams Bay, Wis., where he began developing a photographic method of determining parallaxes. With great care he worked to eliminate or compensate for all significant sources of error, with such success that his photographic parallax measurement techniques remain largely unchanged to the present day. While serving as director (190520) of the Allegheny Observatory, Pittsburgh, Schlesinger obtained a long-focus refracting telescope especially designed for parallax determinations. He published the parallaxes of 7,534 stars in his General Catalogue of Parallaxes (2nd ed., 1935). In addition to his parallax work at Allegheny, Schlesinger also pioneered in the use of wide-angle cameras for determining photographically stellar positions and proper motions (the apparent rates of change of position across an observer's line of sight), formerly measured by laborious visual methods. Fifteen volumes of the Yale Zone Catalogues, which were prepared under his direction, give results for about 150,000 stars. Schlesinger became director (192041) of the Yale University Observatory and continued his parallax work. He also had a prominent role in the establishment of the International Astronomical Union (1919) and served as that organization's vice president (192532) and president (193235).