W. M. Keck Observatory
The Keck observatory domes atop Mauna Kea
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| Organisation | California Association for Research in Astronomy dba W. M. Keck Observatory |
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| Location(s) | 65-1120 Mamalahoa Hwy., Kamuela, Hawaii, United States |
| Coordinates | 19°49′35″N 155°28′30″W / 19.82636°N 155.47501°WCoordinates: 19°49′35″N 155°28′30″W / 19.82636°N 155.47501°W |
| Altitude | 4,145 m (13,600 ft) |
| Wavelength | Optical, near-infrared |
| Built | Keck I 1993, Keck II 1996 |
| Telescope style | Reflector |
| Diameter | 10 m (33 ft) each |
| Angular resolution | 0.04 to 0.4 arcseconds for individual telescopes, depending on target and instruments used |
| Collecting area | 76 m2 (820 sq ft) each |
| Focal length | 17.5 m (f/1.75) |
| Mounting | Alt/az |
| Enclosure | Spherical |
| Website | www.keckobservatory.org |
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The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes feature 10 m (33 ft) primary mirrors, currently among the largest astronomical telescopes in use. The combination of an excellent site, large optics and innovative instruments has created the two most scientifically productive telescopes on Earth.
With a concept first proposed in 1977, telescope designers at the University of California (Terry Mast) and Lawrence Berkeley Labs (Jerry Nelson) had been developing the technology necessary to build a large, ground based telescope. With a design in hand a search for the funding began. In 1985, Howard B. Keck of the W. M. Keck Foundation gave $70 million to fund the construction of the Keck I telescope. Construction of Keck I began in September 1985, with first light occurring on 24 November 1990 using only nine of the eventual 36 segments. With construction of the first telescope well advanced, further donations allowed the construction of a second telescope starting in 1991. The Keck I telescope began science observations in May 1993, while first light for Keck II occurred on October 23, 1996.
The key advance that allowed the construction of the Keck Observatory's large telescopes was the ability to operate smaller mirror segments as a single, contiguous mirror. In the case of the Keck Observatory telescopes each of the primary mirrors is composed of 36 hexagonal segments that work together as a single unit. Each segment is 1.8 meters wide, 7.5 centimeters thick, and weighs half a ton. The mirrors were made from Zerodur glass-ceramic by the German company Schott AG. On the telescope, each segment is kept stable by a system of active optics, which uses extremely rigid support structures in combination with three actuators under each segment. During observation, the computer-controlled system of sensors and actuators adjusts the position of each segment, relative to its neighbors, to an accuracy of four nanometers. This twice-per-second adjustment counters the effect of gravity as the telescope moves, in addition to other environmental and structural effects that can affect the mirror shape.
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