Southern African Large Telescope

11 meters (433 inches or 36 ft)


Summary; History; Current; Technical; Sources; Links; Gallery:

In brief

Important  Contributions:

Largest Telescope in South Africa

Historical Background

More information:

  • Largest  Telescope in South Africa.
  • The  instrument weighs 82 tons.
  • The S.A.L.T. telescope is based on the Hobby-Eberly telescope at McDonald Observatory in Texas USA.
  • The  mirror is eleven meters in diameter. To build a telescope this size demands that it needs to be a reflecting telescope, i.e. mirror telescope, as a refracting telescope (lens with accompanying tube) will be too heavy, impractical and expensive.To build a telescope with an eleven-meter mirror that  is fully movable is prohibitively expensive, as with the KECK and ESO telescopes. The concept behind the Hobby-Eberly  type telescopes, is to have a telescope that is built at a fixed  angle (tilted at 37 degrees), but it can swing around. The telescope is thus only partially movable. The net  result is that 70 % of the sky is observable at a cost of 30 % of the price! Financially it is a winner.
  • Only 70 % of the sky is observable. The trick is to use the  earth’s rotation to help observe the part of the sky you need to go to. This means better planning and scheduling than what  is needed with a fully movable telescope.
  • A movable secondary mirror (Prime Focus Instrument Platform) help to extend the period that any object can be observed.
  • During an observation, the instrument is stationary in azimuth and all  tracking is accomplished by moving the prime focus platform.

An International Joint Venture:

  • S.A.A.O.,  South Africa
  • Nicolaus Copernicus Astronomical Centre in Poland
  • Hobby-Eberley  telescope board, USA
  • Rutgers  University, New Jersey, USA
  • Georg-August Universitat, Germany
  • University of Wisconson-Madison, USA
  • Carnegi-Mellon University, USA
  • New  Zealand University of Canterbury
  • University of North Carolina, USA
  • UK / Irish Consortium

Where  Located:

Current  Information

Present  Location:

Same consortium as given under the Historical Section



Technical  Details

Type: Reflector
Aperture: 11 meters (433 inch or 36 ft)
Focal Length:

  • Primary spherical mirror of 11-m diameter made up of 91 x 1m hexagonal segments. Each 1m segment can tip and tilt and be separately aligned  (adaptive optics).
  • The  telescope does not have a traditional secondary mirror. Instead a highly advanced “Prime Focus Instrument Platform”  is suspended above the primary mirror, which is able to move by  several meters in all directions in order to help track the reflected  light from the celestial source. An annulus of sky 12 degree wide centred 37 degrees from the zenith can be observed for between 48 and 150 minutes during one night.

Mounting: Mounting is fixed in the vertical at an angle of 37 degrees. The instrument can move 360 degrees in the azimuth.  (The mounting can’t move up and down but it can swing around)
Operational History:



Pictorial  Sources:


  • Smits  P. A Brief History of Astronomy in Southern Africa. (Unpublished).
  • “SALT  Ground – breaking Ceremony”, and “Fact Sheet on SALT” , MNASSA, Vol. 59, Nos. 9 & 10, October 2000.