The Crossley telescope is an 36-inch (910 mm) reflecting telescope located at Lick Observatory in the U.S. state of California.
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Given to the observatory in 1895 by British politician Edward Crossley, it was rebuilt from the ground up as it was on a very flimsy mounting. It is still being used today in the search for extra-solar planets. The mirror, and some of the initial mounts came from the 36 inch reflector originally mounted in Andrew Ainslie Common's back yard Ealing obsevatory, who had used it from 1879 to 1886 to prove the concept of long exposure astrophotography (recording object too faint to be seen by the naked eye for the first time). Common sold it to Crossley who had it until 1895.
Observations by James Keeler helped establish large reflecting telescopes with metal coated-glass mirrors as astronomically useful, as opposed to earlier cast speculum metal mirrors. Great refractors were still in vogue, but the Crossley reflector foreshadowed the success of large reflectors in the 1900s. Other large reflectors followed such as the Harvard 60-inch Reflector, also with a mirror by A.A. Common and the Hamburg Observatory Hamburg Spiegelteleskop 1 meter (39.4 in) reflector.[1]
Nicholas Mayall was a long time user of the Crossley and added a slitless spectrograph to extend its usefulness in the face of larger telescopes.