Keck Observatory, an astronomical observatory on Mauna Kea, in Hawaii. The observatory is home to two identical optical telescopes, Keck I and Keck II. They are the largest optical telescopes in the world.

Each telescope is about 81 feet (24.6 meters) tall and weighs 298 tons (270 metric tons). Each gathers light from distant celestial objects by means of a huge mirror some 33 feet (10 m) in diameter. The mirrors are comprised of 36 hexagonal sections about 6 feet (1.8 m) in diameter. An array of instruments in the telescopes analyzes infrared as well as visible light. An interferometer---an instrument that combines light from the two telescopes to achieve highly detailed observations---began operation in 2001.

Research carried out with the Keck telescopes includes the study of galactic clusters, the search for planets outside the solar system, and the analysis of stars' spectra. Astronomers have used this data to further their understanding of the age, composition, and origin of the universe.

Keck I began observations in May, 1993, and Keck II in October, 1996. The observatory was established with a grant from the W. M. Keck Foundation, and it is operated by the California Association for Research in Astronomy for the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration (NASA).