CAPE TOWN, SOUTH AFRICA--Thebe Medupe takes a stroll under the brilliant southern sky, a protective hand on the shoulders of two of his astrophysics graduate students. Although Medupe turned 30 years old this year, his smooth, round face and unconstrained grin make him look more like a classmate of the two youngsters than their supervisor. It wasn't long ago that he was in their position, but they will not face the kind of obstacles that stood in his way.

In 1986, Medupe was 13 years old and living in a village with no running water outside Mafikeng in northern South Africa. This was the year that Halley's Comet came whipping through the solar system, firing Medupe with a passion for astronomy. Straightaway he built his own telescope--using a metal pipe that he cut and fitted with a pair of lenses borrowed from his school--and meticulously mapped the surface of the moon. "I was determined to become an astronomer," recalls Medupe.

Apartheid began to crumble just as Medupe was applying to universities, enabling him to become the first black astronomy student at the prestigious University of Cape Town (UCT). He stayed on to earn a cum laude distinction for his master's thesis and complete a Ph.D. on the interior structure of stars, and now he works at the South African Astronomical Observatory in Sutherland, where he continues to study stellar interiors.

Medupe has also taken on a mission: to attract black students into his field. Astronomy is one of the research communities in South Africa in which black scientists are most underrepresented, with only three among the country's 50 astronomers. Medupe sees two major barriers to transforming these demographics. There is little public outreach to attract black students into astronomy, he says, and those who do take it up "have no black role models to encourage them to go further." Medupe is tackling both these problems at once. "Thebe is an inspiration," beams Brian Warner, head of UCT's astronomy department.

"During apartheid," Medupe says, "we were told that Africans have never been interested in science, and certainly not astronomy." To put the lie to this misrepresentation, Medupe teamed up with a pair of filmmakers and in 2002 traveled across Africa, visiting remote villages and collecting cosmological mythologies. The making of the film, called Cosmic Africa, transformed Medupe. "I know so much about the stars, yet I know so little about my own continent and how my own people are connected to the sky," he explains. The film has won praise at festivals in South Africa and later this month will be aired at the Hayden Planetarium in New York City.

Meanwhile, Medupe is guiding as many black astronomy students into postgraduate research as he can. In 2000, he set up a theoretical astrophysics research program back home at North West University in Mafikeng. When it started, the program didn't even have a room allocated to it--it "really was theoretical," quips Medupe. Four years later the program has plenty of room, including a new computer lab, and Medupe oversees a budding group of two master's and two Ph.D. students. And this year, Medupe is helping run a national program to pluck out the brightest astronomy students--particularly black postgrads at disadvantaged universities--and give them year-round access to the best teaching and research resources.

Medupe has high hopes that his efforts will bear fruit. "My dream is to start seeing top-quality black astronomy graduates running the facilities here," he says, "and participating on an equal basis with astronomers from around the world." It's unclear when that vision will be realized, but Warner believes it is inevitable. "You want to keep your standards high and hire on the basis of skill. So we need to increase the number of qualified black students."

In spite of Medupe's unbridled optimism, one thing still frustrates him. "I go to international astronomy conferences, and I'm almost always the only black face in the crowd." If he gets his way, Medupe will change that.

John Bohannon, a regular contributor to Science, writes from Cambridge, Massachusetts.