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 Hawai'i. The primary mirrors of each of the two telescopes are 10 metres (33 ft) in diameter, making them the second largest optical telescopes in the world, slightly behind the Gran Telescopio Canarias. The telescopes can operate together to form a single astronomical interferometer.
In 1985, Howard B. Keck of the W. M. Keck Foundation gave $70 million to fund the design and construction of the Keck I Telescope. The key advance that allowed the construction of the Keck's large telescopes was the ability to operate smaller mirror segments as a single large mirror. In the case of the Keck each of the primary mirrors is composed of 36 hexagonal segments that work together as a single piece of reflective glass. The mirror is made of Zerodur glass-ceramic by the German company Schott AG. On the telescope, each segment is kept stable by a system of active optics: extremely rigid support structures and adjustable warping harnesses. During observing, a 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 varying distortions due to gravity.
Each Keck telescope sits on an altazimuth mount. Extensive computer analysis determined that this mounting style provides the greatest strength and stiffness for the least amount of steel, about 270 tons per telescope. The total weight of each telescope is about 300 tons.
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.
Both Keck telescopes are equipped with adaptive optics, which compensates for the blurring due to atmospheric turbulence. The first AO system operational on a large telescope, the equipment has been constantly upgraded to expand the capability. Only the Keck 2 Telescope currently has a laser reference star available for use with the AO system. A laser is currently being installed in Keck 1 with first light expected late in 2009.
In addition, the Keck I and Keck II telescopes can work together as the Keck Interferometer. The 85-metre (280 ft) separation between the two telescopes gives them the effective angular resolution in one direction of an 85-metre (280 ft) mirror. Along this axis, the Keck Interferometer has a spatial resolution of 5 milliarcseconds (mas) at 2.2 micrometres (µm), and 24 mas at 10 µm. In its most sensitive configuration, the interferometer would reach K=21 and N=10 mag in 1000 seconds of integration (SNR = 10 per baseline). The interferometer has several back-end instruments, allowing for a variety of observation types. The lack of additional outrigger telescopes makes the Keck Interferometer unsuitable for interferometric imaging, so work has concentrated on nulling interferometry and angular diameter measurements instead. In September 2005, the Keck Interferometer demonstrated nulling interferometry for the first time, with a modest null depth of 100 times.
The Keck Observatory is managed by the California Association for Research in Astronomy, a non-profit 501 (c)(3) organization whose board of directors includes representatives from Caltech and the University of California. Construction of the telescopes was made possible through private grants totaling more than $140 million provided by the W. M. Keck Foundation. The National Aeronautics and Space Administration (NASA) joined the partnership in October 1996, at the time Keck II commenced observations. The Keck I telescope had begun observations in May 1993.
Telescope time is allocated by the partner institutions. Caltech, the University of Hawai'i System, and the University of California accept proposals from their own researchers. NASA accepts proposals from researchers based in the United States, while the National Optical Astronomy Observatory (NOAO) accept proposals from researchers around the world.