MOUNT WILSON OBSERVATORY

astronomical observatory located atop Mount Wilson, about 16 km (10 miles) northeast of Pasadena, Calif., U.S. It was founded in 1904 by George Ellery Hale, who served as its first director. For years the Mount Wilson Observatory and the Palomar Observatory (q.v.), near San Diego, were operated jointly as the Hale Observatories by the Carnegie Institution of Washington in Washington, D.C., and by the California Institute of Technology in Pasadena. In 1980 the two observatories became separate units, with Mount Wilson coming under the administrative control of the Carnegie Institution. The Mount Wilson Observatory houses an array of optical telescopes. The most significant of these is a pair of reflectors, one with a diameter of 1.5 m (60 inches) and the other with a diameter of 2.5 m (100 inches). The latter enabled Edwin P. Hubble and his associates to make important discoveries about the universe, notably its expansion and size. Other major instruments at the observatory include two solar telescopes, which are used to study such phenomena as magnetic fields on the surface of the Sun. Additional reading