Anglo-Australian Telescope

The Anglo-Australian Telescope (AAT) is a 3.9 m equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia at an altitude of a little over 1100 m. In 2009, the telescope was ranked as the 5th highest-impact of the world's optical telescopes. In 2001-2003, it was considered the most scientifically productive 4 metre-class optical telescope in the world based on scientific publications using data from the telescope. The telescope was commissioned in 1974 with a view to allowing high quality observations of the sky from the southern hemisphere (at the time, most major telescopes were located in the northern hemisphere).

It was constructed by Australia and the United Kingdom but has been entirely funded by Australia since 2010. Observing time is available to astronomers worldwide.

The AAT was one of the last large telescopes built with an equatorial mount. More recent large telescopes have instead adopted the more compact and mechanically stable altazimuth mount. The AAT was however one of the very first telescopes to be fully computer-controlled, and set new standards for pointing and tracking accuracy.