born June 29, 1868, Chicago, Ill.
died Feb. 21, 1938, Pasadena, Calif., U.S.
U.S. astronomer.
He studied at Harvard and in Berlin. In 1888 he organized the Kenwood Observatory in Chicago. In 1892 he joined the faculty of the University of Chicago and began organizing the Yerkes Observatory, of which he was director until 1904; there he built the 40-in. (1-m) refracting telescope that remains the largest of its type in the world. He established the Astrophysical Journal in 1895. In 1904 he organized the Mount Wilson Observatory and was its director until 1923. There he built solar apparatus of great power as well as the huge 60-in. (1.5-m) and 100-in. (2.5-m) reflecting telescopes. In 1928 he began work on a 200-in. (5-m) reflecting telescope at Caltech's Palomar Observatory ; completed in 1948, it was named in his honour. As a researcher, he is known particularly for his discovery of magnetic fields in sunspots.