On a hilltop in a nature reserve in the Northern Cape, near the small town of Sutherland, is a masterpiece of modern astronomical engineering. The Southern African Large Telescope (SALT) is the largest optical telescope in the southern hemisphere, and equal to the largest in the world.
Gathering more than 25 times as much light as any existing African telescope, SALT can detect objects as faint as a candle flame on the moon.
Opened in November 2005, SALT is one of the leading instruments of its kind, enabling local and international scientists to see distant stars, galaxies and quasars a billion times too faint to be visible to the naked eye.
The 82-ton telescope is similar to the Hobby-Eberly Telescope in Texas, but has a redesigned optical system – an achievement of South African astronomer Dr Darragh O’Donoghue – that uses more of its mirror array.
Eleven metres in diameter, this array enables imaging, spectroscopic, and polarimetric analysis of the radiation from astronomical objects out of reach of northern hemisphere telescopes.
SALT is a facility of the South African Astronomical Observatory (SAAO), the country’s national optical observatory. With its advanced astronomical technology, it became an icon for what could be achieved in science and technology in South Africa.
- Visit the SA Astronomical Observatory website
The South African Astronomical Observatory has installed live-feed webcams at the SALT site in Sutherland. You can view them here:
Funding and partners
A talented team of local engineers and scientists succeeded in building SALT on a rapid – for big telescope projects at least – five-year timescale. The cost of construction was kept to within the original budget of US$20-million defined in 1998, even before the final designs were completed.
The cost of the construction and operation of the telescope over its first 10 years is a total of US$36-million: US$20-million for the construction of the telescope, US$6 million for instruments and US$10-million for operations. A third of this funding is from South Africa, and rest from the project’s partner countries: Germany, Poland, the United States, the United Kingdom and New Zealand.
About 60% of SALT’s components, including the aluminium dome, were made in South Africa, while construction was carried out exclusively by South African contractors.
SALT’s institutional partners include: National Research Foundation (SA), Nicolaus Copernicus Astronomical Center (Poland), Hobby-Eberly Telescope Board (International), Rutgers University (USA), Georg-August-Universitat Gottingen (Germany), University of Wisconsin – Madison (USA), Carnegie Mellon University (USA), University of Canterbury (New Zealand), Consortium of UK Universities and Institutions, University of North Carolina – Chapel Hill (USA), Dartmouth College (USA), Inter-University Centre for Astronomy and Astrophysics (India), and the American Museum of Natural History (USA).
Building the telescope
In the year 2000, on the first day of southern hemisphere spring, a few hundred people gathered on the hilltop near Sutherland for the SALT ground-breaking ceremony. After nearly four years of construction, in March 2004, installation of the massive mirror began. The last of the 91 smaller mirrored hexagon segments was put in place in May 2005.
First light with the full mirror was declared on 1 September 2005, with the telescope obtaining images of globular cluster 47 Tucanae, open cluster NGC6152, spiral galaxy NGC6744, and the Lagoon Nebula being obtained. SALT was officially opened by then- President Thabo Mbeki on 10 November 2005.
Both SALT and the Hobby-Eberly Telescope have unusual designs for optical telescopes. The primary mirror is composed of an array of mirrors designed to act as a single larger mirror. Each SALT mirror is a hexagon, one metre in size, with the array of 91 identical mirrors together making a hexagonal-shaped primary mirror 11 metres by 9.8 metres in size.
Each of the smaller mirrors can be adjusted in order to properly align to make them function as a single mirror.
SALT’s instrumentation for includes the SALT Imaging Camera (SALTICAM), designed and built by the South African Astronomical Observatory; the Robert Stobie Spectrograph, a multi-purpose longslit and multi-object imaging spectrograph and spectropolarimeter, designed and built by the University of Wisconsin-Madison, Rutgers University, and SAAO; and a fibre-fed High Resolution Spectrograph, designed by the University of Canterbury, New Zealand.
The telescope is connected to the SAAO site in Cape Town via a 10 gigabit per second (gbps) fibre optic connection over the SA National Research Network, a high-speed network that aims to connect 200 research and tertiary sites around South Africa as well as with international research and education organisations.
The major telescopes of the SAAO operate from Sutherland, around 370km from Cape Town and 1800 metres above sea level. This small village is in the Northern Cape, a semi-desert region which is far less developed than the rest of South Africa, with its vast stretches of arid bushland between its cities and towns.
It is the emptiness that is the reason the province has become a major hub for astronomical observations – there’s little artificial light, pollution, or radio waves to interfere with optical and radio astronomy.
In addition to its remoteness, the Northern Cape has a low topography that is well suited to radio astronomy, with mountains providing extra shielding against radio waves from distant metropolitan areas.
The southern hemisphere is the perfect place for astronomy because it sees more of the sky than the northern hempishere. And South Africa’s sophisticated infrastructure and first-class science and technology sector give it the capacity for some of the best astronomical opportunities in the world.
Research using SALT has led to SAAO to many important discoveries, including evidence for a very strange new planetary system, where two giant planets are orbiting a close pair of “suns”.
The observatory can be visited either during the day or at night. A day tour will take you through the visitor’s centre and to designated research telescopes, including SALT.
Ninety-minute night tours include the viewing of interesting objects in the sky through two dedicated visitor telescopes, 16″ Meade and 14″ Celestron. Visitors cannot visit any of the research telescopes at night, including SALT.
- Visit the visitor’s section on the SAAO website for more information on tours
A version of this article was first published on MediaClubSouthAfrica
Last reviewed: 14 June 2012
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