Tyson's interest in astronomy began at the tender age of 9 when he visited the Hayden Planetarium for the first time (yes, the same Hayden Planetarium he's run since 1996). By 11, he was dragging telescopes to the rooftop of his building in Brooklyn. He gave his first lecture in astronomy at 15 [source: Cahalan].
At age 17, Tyson was accepted to Cornell University and shortly thereafter received a letter from one of the university's most famous faculty members, Carl Sagan, who invited him to visit and tour the astronomy lab. As Tyson later recounted, that meeting continues to impact his life today.
"He met me on a Saturday morning in the snow, gave me a tour of his lab... then drives me to the bus station. It's snowing a little heavier -- he writes his home phone number on a sheet of paper, [and] said, "If the bus can't get through, call me, spend the night at our place,'" Tyson remembered. "To this day, I have this duty to respond to students who are inquiring about the universe as a career path in the way Carl Sagan responded to me."
Although Tyson ultimately opted to attend Harvard (because it had a larger astronomy department), he stayed in touch with Sagan throughout his life [source: Arizona Horizon].