The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 1,740-metre peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles.
The observatory contains two historically important telescopes: the 100-inch Hooker telescope, which was the largest aperture telescope in the world from its completion in 1917 to 1949, and the 60-inch telescope which was the largest operational telescope in the world when it was completed in 1908. It also contains the Snow solar telescope completed in 1905, the 60 foot solar tower completed in 1908, the 150 foot solar tower completed in 1912, and the CHARA array, built by Georgia State University, which became fully operational in 2004 and was the largest optical interferometer in the world at its completion.
Due to the inversion layer that traps warm air and smog over Los Angeles, Mount Wilson has steadier air than any other location in North America, making it ideal for astronomy and in particular for interferometry.