Crossley telescope, Reflecting telescope at Lick Observatory, Santa Clara County, United States

The Crossley telescope is a 36-inch (910 mm) reflecting telescope at Lick Observatory on Mount Hamilton, California. Its mirror, made by George Calver for Andrew Ainslie Common, came from Common's Ealing observatory, and the instrument was rebuilt from the ground up after Edward Crossley donated it in 1895 because its original mounting was very flimsy.

Built by Andrew Common in 1879, the telescope was later given to the observatory by Edward Crossley. It changed how astronomers could photograph distant stars that were too faint to see directly.

The Crossley's name honours Edward Crossley, the British politician who donated it in 1895. Its mirror came from Andrew Ainslie Common's Ealing observatory, where from 1879 to 1886 he used it to prove long-exposure astrophotography could record objects too faint for the naked eye. Lick director James Edward Keeler called it, in 1900, "by far the most effective instrument in the Observatory for certain class of astronomical work."

The Crossley is housed in a dome at Lick Observatory on Mount Hamilton, reached by a winding road east of San Jose. It has been out of service since 2010 because of budget cuts, so it is seen as a historic instrument rather than used for observing. Check observatory opening times before travelling.

The mirror received multiple coating upgrades, shifting from silver to aluminum between 1934 and 1951 through specialized processes that improved its light-gathering ability. These refinements allowed it to capture images of fainter celestial objects than ever before.