Light from the Lagoon Nebula had to cross about 3,800 light-years before it reached the virgin mirror of the South African Large Telescope this summer.

	South African Large Telescope Observatory This image of the Lagoon Nebula is among the "first light" images released from SALT. Click photo for larger image.

By comparison, the 8,000 miles separating the telescope from Pittsburgh is hardly worth mentioning. And from the perspective of Richard Griffiths, an astrophysicist at Carnegie Mellon University, it really doesn't matter that SALT is a hemisphere away.

Carnegie Mellon is one of 11 international partners in the SALT project and, as such, will have guaranteed observing time once the scope is fully operational. So when images of the Lagoon Nebula and several star clusters were released last week, marking what astronomers called the telescope's "first light," Griffiths had reason to be happy.

"The performance is pretty good right now, considering that we are at the start of commissioning," he said of the initial images. It also is encouraging is that the construction has been completed on schedule, just five years after ground breaking in the Karoo region northeast of Cape Town, and within its $20 million budget.

"That's pretty amazing for a big telescope like this," he added.

SALT's primary mirror has 91 mirror segments, forming an array measuring 10 meters by 11 meters. In terms of collecting area, it is the equal of the largest telescopes in the world.

But it also is "relatively cheap," said Griffiths, making it affordable for universities such as Carnegie Mellon to own a piece of it. SALT is an improved version of the Hobby-Eberly Telescope at the McDonald University in Texas, built by a consortium that includes Penn State University.

Unlike conventional astronomical telescopes, which are designed to track objects across the sky all night long, Hobby-Eberly and SALT have stationary mirrors. That limits how long those telescopes can view an object on any single night, but it also eliminates the need for the expensive mechanism that otherwise would be necessary for moving a 90-ton mirror array.

	University of Wisconsin-Madison The South African Large Telescope near Sutherland, South Africa, by the edge of the Kalahari Desert. Click photo for larger image.

The bottom line is that SALT can do many of the same observations as a conventional, 10-meter-class telescope such as the Keck Observatory in Hawaii, but at about one-sixth of the cost.

Astronomers today routinely use a variety of telescopes for their studies, often competing for observing time on both space-based and ground-based scopes, as well as instruments that observe at optical, X-ray, radio or other frequencies. But there are more observing proposals than there is observing time, so guaranteed time on a major telescope is prized.

"Most of the discoveries these days are being made on 10-meter telescopes," said Eric Wilcots, an astronomer at the University of Wisconsin. That's why Wisconsin, which already has a quarter share in a 3.5-meter telescope on Arizona's Kitt Peak, opted to join the SALT consortium five years ago.

Wisconsin, which is helping to build and install a spectroscopic imaging device that will be SALT's primary instrument, has a 15 percent share of the telescope. Carnegie Mellon, which initially was projected to be a major partner, ultimately scaled back its commitment to $1 million, buying a 3 percent share of the telescope's observing time for the next 10 years.

In addition to the National Research Foundation of South Africa, other members of the consortium include Rutgers University, Dartmouth College, and the University of North Carolina. The project is budgeted to cost $32 million for construction and the first 10 years of operations.

Griffiths said Carnegie Mellon has paid about two-thirds of its contribution to SALT thus far.

Though the university has only a small share of the observing time, Griffiths said that is still significant because he and his graduate and post-graduate associates will be the primary users from Carnegie Mellon.

Like other users, Griffith won't need to travel to South Africa to use the telescope. His observations will be carried out by the on-site staff and the raw data sent to him over the Internet.

Once the telescope is dedicated in November and is fully operational, Griffiths plans to use it to do optical studies of distant clusters of galaxies that he has discovered with X-rays using the orbiting XMM Newton telescope.

Griffiths is interested in analyzing those clusters to determine what fraction of the X-ray emissions he has recorded are coming from quasars and active galaxies. By subtracting out X-rays from those sources, he hopes to be able to use the distribution of galactic clusters as a way of measuring "dark energy," the mysterious force thought to be accelerating the expansion of the universe.

"It's the hot gas [in the clusters] we need to measure for the dark energy," he explained. "The quasars are kind of a nuisance factor."