In 2000, South Africa and its international partners joined forces to build the largest single optical telescope in the southern hemisphere, with a hexagonal mirror array 11 metres across. An observation required the primary mirror to be stationary and the instruments move across on a tracker, which follows the Earth's rotation. The Southern African Large Telescope (SALT) is situated alongside the telescopes of the South African Astronomical Observatory (SAAO) on a hilltop close to Sutherland in the Northern Cape Province.