Palomar Observatory, an observatory on Palomar Mountain northeast of San Diego. It houses the Hale telescope, which has a mirror 200 inches (508 cm) in diameter. The telescope was dedicated in 1948 and was the largest reflecting telescope in the world until the completion in 1975 of a 236-inch (600-cm) reflecting telescope in the Soviet Union. The Palomar Observatory also has a 48-inch (122-cm) Schmidt telescope and several smaller telescopes.

Palomar Observatory is owned and operated by the California Institute of Technology. Cornell University and the Carnegie Institution of Washington share in the use of the Hale telescope.

Research at Palomar is primarily concerned with the farthest reaches of space. Its astronomers study such problems as the structure of galaxies, the nature of quasars, and the expansion of the universe.