The board of the TMT Observatory Corp., based in Pasadena, Calif. (U.S.A.), announced today that it chose Mauna Kea to build the 30-m-wide segmented-mirror telescope over Cerro Armazones in Chile’s Atacama Desert. The TMT team had narrowed its list of potential sites from five to those two in May 2008.

With a summit of 4,205 m above sea level, Mauna Kea already hosts some of the world’s finest observatories, including the twin 10-m Keck telescopes, which are connected with a fiber link for interferometric observations; the Japanese Subaru telescope; and one of the twin multinational Gemini telescopes (the other is in Chile).

TMT board chair Henry Yang, chancellor of the University of California at Santa Barbara (U.S.A.), said both site finalists could provide high-quality astronomical observations. However, Mauna Kea edged out the Chilean plateau because of its higher altitude, lower humidity, smaller temperature variation and greater atmospheric steadiness.

The Keck telescopes, with their primary mirrors composed of 36 hexagonal segments in computer-controlled alignment, were considered revolutionary when they opened for business in the mid-1990s. TMT is the same concept on steroids: its 492 1.66-m hexagonal segments will stretch a total of 30 m across. Astrophysicist Jerry Nelson, who spearheaded the Keck design, serves as TMT’s project scientist.

Thus, TMT will look a little different from the subject of OPN’s July/August cover story, the Giant Magellan Telescope (GMT), which will feature seven of the largest mirror segments that can be made. Both, however, are part of the next generation of 25- to 40-m telescopes that likely will make the big astronomical discoveries of the third decade of the 21^st century. The European Space Organization is planning a highly segmented Keck-style 40-m instrument called the European Extremely Large Telescope (E-ELT).

When completed in 2018, the TMT will sit on a plateau a bit below the main Mauna Kea summit area on the western side of the mountain. Its fast f/1.0 primary will allow its enclosure to be as compact as possible.

Assuming the Hawaiian site receives its final land-use permits, site construction could begin in 2011, according to Yang.

TMT is mostly a North American project; its partners are Caltech, the University of California and the Association of Canadian Universities for Research in Astronomy. The National Astronomical Observatory of Japan is listed as a collaborating institution. Several public and private organizations in the United States and Canada have provided funding for the design stage.

I’ve actually visited the summit of Mauna Kea in preparation for my September 2007 OPN feature on ground-based telescopes. It is an awesome place, literally above most of the clouds, with a sky deeper blue than at sea level. I look forward to many exciting astronomical discoveries in the future.