Astronomical observatory located atop Mount Wilson, near Pasadena, California, U.S. Founded in 1904 by George Ellery Hale (18681938), it was operated jointly with Palomar Observatory as Hale Observatories (194880).
Its largest optical telescope, with a diameter of 100 in. (2.5 m), enabled Edwin Hubble and his associates to discover evidence of an expanding universe and to estimate its size.