Mount Wilson Observatory is an observatory at an altitude of 1,740 meters on Mount Wilson in the San Gabriel Mountains near Pasadena, California, about 30 kilometers northwest of Los Angeles. It was founded in 1904 by George Hale and is owned by the Carnegie Institution of Washington, DC.

The main nighttime telescopes of the Mount Wilson Observatory are a 60-inch (1.5-meter) reflector, built in 1908, and the famous 100-inch (2.5-meter) Hooker Telescope, built in 1917. Two solar observatories, the 60-foot tower telescope (operated by University of Southern California) and the 150-foot tower telescope (operated by the University of California at Los Angeles), maintain long-term exploration of the magnetic activity behavior of the Sun. There are also two interferometers on the site: the Infrared Spatial Interferometer (ISI, operated by the University of California at Berkeley) and the NRL Optical Interferometer.