SALT sees first light

A cutting-edge telescope in South Africa is now operational, providing astronomers unprecedented access to the southern sky.
By | Published: September 1, 2005 | Last updated on May 18, 2023

The Lagoon Nebula
The Lagoon Nebula was among SALT’s targets when the telescope saw first light. Spectroscopic measurements using the telescope’s main scientific instrument, the PFIS, may help astronomers understand how such emission nebulae form.
Southern Africa Large Telescope (SALT) project
September 1, 2005
The South African Large Telescope (SALT) released its first images today. Five years after construction began, the scope made its first observations, termed “first light,” from its dark-sky perch at the edge of the Kalahari Desert in South Africa.

“The declaration of first light signifies SALT has arrived on the astronomical scene,” the South African Astronomical Observatory, SALT’s parent organization, expressed in a statement. The scope joins six others at the mountaintop site, but the megalith boasts a primary mirror array 32 by 36 feet (10 by 11 meters), making it the largest telescope in the Southern Hemisphere.

The South African Large Telescope
This 2003 image shows the South African Large Telescope (SALT) as it nears completion outside Sutherland, South Africa. The instrument now holds 91 mirror segments — 84 more than it did when this photograph was shot.
Jian Swiegers, SALT Project Team
Each of the 91 mirrors contains three computer-controlled edge sensors that maintain the segment’s position with neighboring panels as the base moves or the temperature changes. This unique design delivers a light-gathering power that rivals the world’s largest optical scopes; SALT could detect a candle flame on the Moon.

The images, taken with a digital camera called SALTICAM, include the Lagoon Nebula, globular cluster 47 Tucanae, and spiral galaxy NGC 6744. “The southern Milky Way is more spectacular and provides a richer treasure trove of objects than the northern Milky Way,” comments project member Eric Wilcots of the University of Wisconsin, Madison.

Studies are already planned to explore stars in the Large and Small Magellanic Clouds — the closest galaxies to the Milky Way, and best seen in the southern sky — to better understand galactic evolution. Other projects include ultraviolet observations of stars using the main scientific instrument, the Prime Focus Imaging Spectrograph (PFIS).

47 Tucanae
SALT imaged 47 Tucanae, a globular cluster located in the southern-sky constellation Tucana.
Southern Africa Large Telescope (SALT) project
Installation of the PFIC is slated for mid-September. Once in place 10 stories above the primary mirror, the spectrograph will enable researchers to study starlight from a swath of sky. The telescope’s base moves to select an area of sky for observation, and instruments at the top move to track specific objects. “With traditional instruments, we see one star at a time. With PFIS, we’ll capture data on 1,000 stars simultaneously,” notes Carlton Pryor, a project member from Rutgers University.

In addition to the telescope’s size and advanced technology, its location is a boon. Project member Theodore Williams, also of Rutgers, explains, “For the first time, astronomers can now have a detailed 24-hour view of the southern night sky by combining South African observations with similar images from telescopes in Australia and Chile.”

SALT is supported by 11 partners worldwide.

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