High Quality Content by WIKIPEDIA articles! 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. According to a Sydney Morning Herald article, in 2009 the telescope was ranked 5th out of the world`s optical telescopes, and was considered the most scientifically productive optical telescope in the world. 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).