Overview::W. M. Keck Observatory


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Overview With a concept first proposed in 1977, telescope designers at the University of California and Lawrence Berkeley Labs 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 March 1993, while first light for Keck II occurred in 23 January 1996.

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The Keck II Telescope showing the segmented primary mirror

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. The mirrors were made from Zerodur glass-ceramic by the German company Schott AG.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.

Each Keck telescope sits on an altazimuth mount. Most current 8–10 m class telescopes use altazimuth designs due to the reduced structural requirements compared to older equatorial designs. This mounting style provides the greatest strength and stiffness for the least amount of steel, which, for Keck Observatory, totals about 270 tons per telescope. The total weight of each telescope is more than 300 tons. Two of the proposed designs for the next generation 30 and 40 m telescopes use the same basic technology pioneered at Keck, a hexagonal mirror array coupled with an altazimuth mounting.

The primary mirrors of each of the two telescopes are 10 meters (32.8 ft (394 in)) in diameter, slightly smaller than the Gran Telescopio Canarias. However, all of the light collected by the Keck Observatory primary mirrors (75.76 m2) is sent to the secondary mirror and the instruments, compared to GTC's primary mirror, which has an effective light-collection area of 73.4 m2, or 25.4 square feet less than each of the Keck Observatory primary mirrors.

Because of this fundamental difference in design, Keck Observatory's telescopes arguably remain the largest steerable, optical/infrared telescopes on Earth.

The telescopes are equipped with a suite of instruments, both cameras and spectrometers that allow observations across much of the visible and near infrared spectrum.

W. M. Keck Observatory sections
Intro   Overview    Management    Instruments    See also   References  External links  

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