The largest single optical telescope in the southern hemisphere, SALT has a hexagonal mirror array, with a diameter of 11 metres. This mirror is made up of 91 individual 1.2m hexagonal mirrors, each of which weighs approximately 100 kg. These segments can be positioned and adjusted individually by means of actuators; this occurs in response to feedback from edge sensors, which can detect even the tiniest changes in the relative positions of the mirror segments. About once a week, a sensor in the high tower is used to align all of the mirror segments to an ideal spherical surface.
Because SALT is so large inside, it was difficult to get a good photograph, what with all the struts and beams and structures everywhere. But you can still see the segmented mirror behind me.
Luckily, there is a model of the inside of the telescope in the Museum at the Visitors’ Centre, which is where I took the photo below. This gives you a better idea of what it looks like inside.
Astronomers and students wishing to make use of SALT need to apply months in advance to be allocated time. Given the accuracy and quality of this instrument, its ideal location in an isolated area, far away from light pollution, and the fact that Sutherland had clear dark skies and a predominantly dry climate year-round, it is always in high demand.
I think it is fabulous that South Africa has such excellent astronomy facilities. SALT at the SAAO is only one of many.