A documentary follows Bill Nye’s campaign to debunk climate-change deniers while revealing the beloved scientist’s private life. (Lindsay Mann/Structure Films/Public Broadcasting Service)

Bill Nye, the lanky, bow-tied TV science advocate, is still a hero to a generation of young adults who eagerly watched his 1990s series, “Bill Nye, the Science Guy,” in classrooms or on afternoon television. The fast-paced, half-hour educational show made science fun, with hands-on experiments that kids could replicate at home. Nye also used such thrilling stunts as parasailing to demonstrate wind force, or explained the Earth’s ecosystem while speeding down the road in a grass-covered car.

Today, Nye still uses his unique brand of intellectual showmanship to highlight the importance of science, but as the documentary “Bill Nye: Science Guy” shows, he has shifted his focus from kids to grown-ups. At 61, Nye now wields his infectious enthusiasm to fight against climate-change denial. It’s a fight that has brought him face to face with some prominent skeptics while also winning him legions of new fans and reinforcing the adoration of his old ones.

In the documentary, we see Nye draw passionate crowds at his public appearances, where he’s greeted like a sports star by raucous fans in a college auditorium or followed around, celebrity-style, at a conference for science teachers. Some people are eager to talk about their careers in science — all due to his influence, they say — and to snap photos with their idol. “I’ve been asked to talk about selfie fatigue,” Nye jokes, catching his breath in an elevator. “I’m pretty sure it shortens your life.”

"Bill Nye" alternates compelling glimpses into Nye's psyche with an overview of his campaign to debunk high-profile climate-change deniers such as creationist Ken Ham. These encounters form the backbone of the film. Nye engages Ham, founder of the fundamentalist theme attraction Ark Encounter, in a spirited debate on climate change and global warming. He also tours Ham's exhibitions, shaking his head and declaring that presenting dinosaurs as coexisting with humans constitutes "anti-science."

The film also provides an eye-opening look at the private side of this public crusader. Nye cites his desire to leave the world better than he found it. Being childless, he says he’s motivated by the idea that his work will be his legacy. But we also hear from a lifelong friend, who says that Nye “always wanted to be famous.” Now that he is, his friends and colleagues — and Nye himself — consider how life in the spotlight has changed him.

What hasn’t changed is Nye’s dogged determination to spread the gospel of science. During a college lecture a student asks him about strategies for connecting with science skeptics, and Nye responds: “Just keep talking. Draw them out, and ask why they believe [what they believe]. Try to understand.”

Understanding has always been the cornerstone of Nye’s work. “Bill Nye: Science Guy” offers an absorbing and entertaining portrait, of both the science evangelist and the guy behind him.

Unrated. At Landmark’s West End Cinema. Contains nothing objectionable. 101 minutes.