Anglo-Australian Telescope

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The Anglo-Australian Telescope (AAT) is a 3.9-meter optical telescope located at Siding Spring Observatory in New South Wales, Australia, about 1,100 meters above sea level. It is equatorially mounted and was built by a UK–Australia partnership. First light was on 27 April 1974, and it was officially opened by Prince Charles on 16 October 1974. Since 2010, Australia has funded the telescope entirely, and observing time is available to astronomers worldwide. The AAT helped spark renewed British interest in optical astronomy and was the largest telescope in the Southern Hemisphere when it started.

The telescope sits in a seven-story concrete building topped by a 36-meter rotating steel dome. Its tube is supported inside a 12-meter horseshoe that rotates around the polar axis, with a total moving mass of about 260 tonnes. It offers multiple foci to suit different instruments: originally a f/3.3 prime focus, an f/8 Cassegrain, and options for f/15 and f/36. In the 1990s a fourth top-end was added to provide a 2-degree field of view at prime focus, feeding 400 optical fibres for the 2dF instrument, and later used by AAOmega and HERMES. The mirror blank was made in the United States and finished in Britain, while the mount was built by Mitsubishi Electric. The AAT is also noted as one of the last major telescopes built with an equatorial mount and one of the first to be fully computer-controlled.