The TIME 100

You can think of Neil deGrasse Tyson as the Carl Sagan of the 21st century—as long as you envision a Sagan who's muscular, African American and as cool as his predecessor was geeky. While Sagan used to appear on the Tonight Show to chat professorially with Johnny Carson, Tyson trades quips with Jon Stewart and Stephen Colbert. And you can hardly imagine Sagan's being named Sexiest Astrophysicist Alive by PEOPLE magazine (Tyson got the nod in 2000) or declaring, as Tyson once did, that in high school "I was a nerd who could kick your butt."

These minor differences aside, Tyson, 47, is the undisputed inheritor of his late predecessor's mantle as the great explainer of all things cosmic. He has written seven popular books (the latest, Death by Black Hole, was a New York Times best seller); stars in the PBS series Nova Science Now; and, perhaps most important, is the charismatic director of the venerable Hayden Planetarium, at the American Museum of Natural History in New York City. "He's got a larger-than-life personality," says David Spergel, chairman of the department of astrophysics at Princeton University and a onetime colleague of Tyson's on the school's faculty.

Tyson's stay at Princeton was only one stop on his ivy-scattered road—a bachelor's from Harvard and a Ph.D. from Columbia came first—but it was a memorable one. The course he taught there, astronomy for nonscientists, was wildly popular, and that, along with his burgeoning career as an author, is what persuaded the museum to offer him the job. Tyson accepted, on one condition: "I asked them to establish a research department of astrophysics," he says. The museum agreed, and the department is now 14 astrophysicists strong. "If we ever needed a scientifically literate population," says Tyson, "it's now. I get enormous satisfaction from knowing I'm doing something for society." But it's also pretty obvious, watching him in action, that Neil deGrasse Tyson is having a heck of a lot of fun.