The W.M. Keck telescopes are the two largest telescopes of the Mauna Kea Observatory on Mauna Kea in Hawai'i. These are reflecting telescopes located at an altitude of 4,145 m (13,600 ft). Keck I started observing in 1993 and Keck II started in 1996. This is a Ritchey-Chrétien type of telescope on an altazimuth mount, assisted by active optics. The Keck telescopes have, essentially, 10m mirrors; however, rather than having one mirror each telescope has 36 smaller hexagonal mirrors working together. In addition, Keck I and II can work together, via interferometry; this gives them the effective power of an 85m mirror.
