On Friday, July 24 the 10.4-meter Gran Telescopio Canarias (GTC) or Great Canary Telescope will be inaugurated. The GTC is slightly larger than Hawai'i's twin 10-meter Keck telescopes and will now hold the title of world's largest optical telescope.
I had the chance to visit the telescope when I attended the Starlight Conference in 2007.
Unfortunately I did not have a wide-angle lens with me.
That's the view from the observing floor looking up into the dome and the telescope's primary mirror.
Unlike the Hale's monolithic mirror the GTC's primary mirror (like those at Keck) is made up of 36 segments. The segments are just over 3 inches (8 cm) thick. Each of the 36 mirrors must remain properly aligned. Everything that's below the mirror segments in the photo above (except what is red) is part of the GTC active optics system which continuously adjusts the position of the segments to keep them perfectly aligned. Palomar's 200-inch mirror has a primitive version of the same thing. In our case the mirror has 36 supports which are passively controlled. As the telescope moves to a different position they gravitationally readjust their push or pull on the glass to keep it in the proper shape.
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