SALT: Imaging the Southern Sky
When South Africa decided to build a new telescope, it went big. As in rival-the-world's-best big. With the participation of astronomy groups from all over the world, the Southern African Large Telescope, or SALT, is casting a wide eye on the southern sky. Moreover, it's inspiring future astronomers in the region. This feature takes you behind the scenes as this bold new telescope brings world-class astronomy to a developing nation.
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The Shining Star of South African Astronomy
The desert scrubland above the tiny, remote village of Sutherland, South Africa, has a few things that astronomers want. High elevation. Dark skies. Still air. All make for ideal observing conditions: Telescope pictures taken from Sutherland tend to be less spoiled by city lights or Earth’s turbulent atmosphere. On cloudless, moonless nights, the stars are so bright over Sutherland that a person can walk by starlight alone.
Astronomy in South Africa didn’t begin in Sutherland, but it is now flourishing there. In 1820, the British set up the Royal Observatory on the Cape of Good Hope to study celestial objects viewable only from the Southern Hemisphere. In 1972, the Royal Observatory became the South African Astronomical Observatory, which, over the years, has positioned 11 telescopes on the 1,798-meter high plateau near Sutherland. The star of this fleet, the Southern African Large Telescope, was added in 2005. With its massive mirror and distinct geographic advantages, SALT, as it is called, is poised to elevate both South African astronomy and a new generation of space scholars.
SALT’s Star Power
Many of the sky’s most interesting objects can be spotted only from telescopes positioned well south of the equator. These include the Large and Small Magellanic clouds (our two nearest galaxies) and the center of the Milky Way Galaxy, which crests right over Sutherland. Most of the world’s telescopes are in the Northern Hemisphere. Before SALT, the many astronomers wanting to peer precisely at the southern sky had few options save a handful of excellent telescopes in South America.
SALT’s 11-meter mirror makes it the largest optical telescope in the Southern Hemisphere. It rivals Northern Hemisphere counterparts such as the 10-meter telescope at W. M. Keck Observatory in Hawaii and Texas’s Hobby-Eberly Telescope. In astronomy, bigger is definitely better: the larger the mirror, the more light the instrument collects. A massive mirror can do two things quite well, says Phil Charles, the director of the South African Astronomical Observatory. The first is detecting distant, faint objects such as galaxies and quasars. Because their light takes so long to travel across the Universe, SALT’s images can reveal how these objects existed in the early Universea boon for scientists studying the evolution of the cosmos. Secondly, a large mirror can collect a lot of light in a short period of time. “You can study how things vary on short timescales,” says Charles. “That allows you to probe what’s going on in some of the most astrophysically interesting situations.” These situations include binary star systems, where the light changes quickly. SALT also hosts a spectrograph, a device that splits light into its component colors to fingerprint the properties of luminous objects.
The Story of SALT
Before SALT, the largest telescope in South Africa was just shy of 2 meters wide. “It has been operating for about 50 years,” says Patricia Whitelock, an astronomer with the South African Astronomical Observatory and the University of Cape Town. “In fact, when the 1.9-meter telescope came to South Africa, it was the biggest telescope in the Southern Hemisphere. It is now regarded as a small telescope by anybody’s standards. It was quite clear to us that with just a 1.9-meter telescope we were not going to be able to keep up with what was going on in the rest of the world. We were not even going to be a reasonable partner with the rest of the world. We needed a larger telescope.”
Yet there was little possibility of financing a major telescope project during South Africa’s apartheid era. The international community wouldn’t touch the idea of aiding a whites-only scientific enterprise, says Whitelock. After apartheid was dismantled in the early 1990’s, the new government began contemplating a big telescope. The nation could now leverage its geographic advantage, its scientific talent, and the existing infrastructure at Sutherland to find global partners so it could finally partake in world-class astronomy.
With nearly half of South Africans living in poverty, the government appealed to other countries - the United States, the United Kingdom, Poland, and India among them - to foot two-thirds of SALT’s bill in exchange for observation time. To make the observing schedule efficient for all, the observatory runs the instrument much like a space telescope. Astronomers wishing to use SALT don’t travel to Sutherland to observe. Instead, an on-site operator and staff astronomers bundle the requests each night, selecting priority objects that are near one another in a clear patch of sky.
The South African government also capitalized on a nontraditional mirror design developed with much trial and error by Texas’s Hobby-Eberly Telescope. With current technology, it is unfeasible to build a single mirror larger than 10 meters in diameter. So instead of a single reflective surface, 91 smaller segments are pieced together like a puzzle to make a large mirror. In the end, SALT’s 11-meter telescope was built for about $30 million – the price of a traditional 4-meter telescope.
Toward the Future
SALT holds promise not only as an astronomical tool but also as a guiding light for aspiring scientists in this changing nation. This is especially true for black South African students. They remain stung by the legacy of apartheid, under which science education for blacks was deemed unnecessary.
One goal of SALT is to increase the number of black South Africans with astronomy degrees. Ramotholo Sefako, who supervises the smaller telescopes at Sutherland, estimates that the total now is not more than ten. Six years ago, Sefako himself was the first black South African to earn a Ph.D. in astrophysics. “SALT means a lot to me and I think it means a lot to a lot of South Africans as well,” he says. “It shows that science is not only for the elite.” South Africans pursuing Ph.D.’s in astronomy can apply for scholarships to study at SALT partner institutions such as Rutgers University in New Jersey and Southampton University in the United Kingdom. The Sutherland site and educational materials are also used for practical training of astronomy students from all over Africa.
“SALT is a great enabler,” says Kevin Govender, who heads the telescope’s efforts to reach beyond the research community. “There are immediate results in terms of scholarships. But in the long term, we hope to catch students early on and continue a relationship with them, motivate them to science careers down the line so that they contribute to our economy.” Govender orchestrates a panoply of workshops, clubs, stargazing nights, and other events that use astronomy to educate and empower both youth and adults. He is driven by the notion that looking at the stars encourages people to think broadly. “It can motivate you to change your perspective from one of stuff in front of you to one where you look beyond,” he says. “Towards the future.”
The future may bring yet another mammoth sky-scanner to South Africa, the Square Kilometer Array (SKA) radio telescope. It will be 50 times more sensitive than current radio observatories, relying on the cell-phone and radio-interference-free environment of the remote Northern Cape region. That South Africa now has SALT and is on the SKA short list is “wonderful” to Phil Charles. “Just 10, 15 years ago, we couldn’t have dreamed of something like this happening in this country.” Finally, South African astronomers can dream big.