Yale University is the latest institution to buy time on the twin telescopes at the W.M. Keck Observatory atop Mauna Kea.

Under the $12 million deal with the California Institute of Technology, one of the Big Island observatory's partner institutions, Yale astronomers will get 15 nights of observing time annually over 10 years.

Jeffrey Kenney, chairman of Yale's astronomy department, said in a news release that researchers will use the 10-meter telescopes to explore how galaxies evolve in nearby galaxy clusters and study some of the most distant and most massive galaxies in the universe.

Until now, Yale astronomers have relied for the bulk of their observational data on the 3.5-meter WIYN telescope on Kitt Peak in Arizona, which is owned and operated by a consortium that includes Yale, the University of Wisconsin, Indiana University, the National Optical Astronomy Observatory and SMARTS, a collection of smaller telescopes in Cerro Tololo, Chile.

"Access to the Keck telescopes puts the Yale Center for Astronomy and Astrophysics on the same footing as other top astronomy and astrophysics programs in this country," Yale's Meg Urry said in a news release.

Urry is founding director of the Yale Center for Astronomy and Astrophysics and Yale physics department chairwoman.

The Keck Observatory is operated by the California Association for Research in Astronomy, whose board of directors includes representatives from Caltech and the University of California. Its twin telescopes, each standing eight stories tall and weighing 300 tons, are the world's largest optical and infrared telescopes. Each telescope gets its viewing power from a mirror comprising 36 hexagonal segments that work in concert as a single reflective glass surface.

Major discoveries based on Keck observations include the existence and weight of the supermassive black hole at the center of the Milky Way, and the presence of methane and possible signs of life on Mars.

Keck spokeswoman Ashley Yeager said more than half of all planets known outside our solar system have been discovered using observations from the Keck Observatory, which also has played a crucial role in discovering that the universe is not only expanding but that the expansion is accelerating.

In the past fiscal year, 420 scientific investigations were conducted using the Keck telescopes, she said.

Access to the telescopes is highly prized, and the 365 nights of observing time are divided among its partner institutions. Caltech and the University of California are allocated 36.5 percent each of the observing time, the National Aeronautics and Space Administration gets 14.5 percent and the University of Hawai'i 12.5 percent.

DEAL WITH CALTECH

Caltech agreed to sell 15 nights of its viewing time to Yale and has a similar arrangement with Swinburne University of Technology in Melbourne, Australia.

Other institutions can apply for observation time with the Keck partners or through the National Science Foundation's Telescope System Instrumentation Program that is administered by the National Optical Astronomy Observatory.

Astronomers gathering observation data actually do their work at the observatory's headquarters in Waimea while assistants operate the telescopes at the 13,796-foot Mauna Kea summit. The Keck Observatory was the first facility on Mauna Kea to use remote observing.

The clear, calm and dry summit is ideal for astronomy observations because there is little light pollution from populated areas below and no nearby mountain ranges to stir up the upper atmosphere or throw light-reflecting dust into the air.

The observatory was built with a $138 million grant from the W.M. Keck Foundation, with additional funding provided by public and private grants and individual contributions. The Keck I telescope began observations in May 1993, and the Keck II started in October 1996.

The observatory employs 122 workers.

Caltech and the University of California have an agreement to provide annual base operating support for the observatory through 2018. The amount paid in fiscal year 2008 was $11.6 million.

NASA provided $2.3 million in operating support last year, and Yeager said the Observatory signed a new five-year cooperative agreement with the space agency that awards $16.7 million over the next five years for operations support, infrastructure renewal and data archiving.

In addition, new awards in fiscal year 2008 from other public grants and contracts surpassed $8.5 million, Yeager said.