Right before the screening of “Bill Nye: Science Guy,” two familiar-looking men walked into the Wellmont Theater from a side backstage door, and the audience erupted in cheers.

One was Montclair’s own Stephen Colbert.

The other was the Science Guy himself.

Nye was at the Montclair Film Festival on Saturday as part of its “In Conversation” series.

Nye shot to fame in the 1990s with “Bill Nye the Science Guy,” which aired on PBS for five seasons.Today, Nye is the CEO of The Planetary Society, which was founded by Carl Sagan, and host of a new series on Netflix, “Bill Nye Saves the World.” He has also been working to raise awareness of the threats posed by climate change — a job that has gotten more and more challenging over the past few years due to high-profile climate change deniers.

After the documentary screening, Nye and Colbert took to the stage to talk about a variety of things: science education, climate change, why the Pinto was a lousy car, the Planetary Society’s solar-powered LightSail spacecraft project ... and comedy.

“If the microphone were the earth,” Nye said as he was explaining LightSail’s trajectory, “and you were the glory of the sun...”

“Thank you,” Colbert quipped as the audience erupted in laughter.

One recurring theme during the discussion, however, was something serious: concerns over a push-back against science, especially where climate change is concerned, and a persistent strain of anti-intellectualism.

“I saw this on Fox News — Fox Business. More silver bullets are sold during a full moon,” Colbert joked, referring to a commonly held belief that emergency room visits increase during a full moon.

“You’ve got to get to people before they’re 12. Ten is best,” Nye said, referring to the need to get children and young people fascinated by science. “And that’s a hard thing.”

Colbert cited a quotation that is attributed to Isaac Asimov: “There is a cult of ignorance in the United States. Anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that ‘My ignorance is as good as your knowledge.’”

“Bill Nye: Science Guy” is the brainchild of filmmakers Jason Sussberg and David Alvarado. It looks back on Nye’s career as a science educator, advocate and comedian, and brings the viewer up to date on Nye’s more recent work. The film includes interviews by Neil deGrasse Tyson; Ann Druyan, co-producer of Cosmos, and widow of Carl Sagan; and some of the writing and production staff on “Bill Nye the Science Guy.”

The documentary noted that there has been a substantial push-back in politics and the media by climate change deniers, including a steady parade of commentators on Fox News; Ken Ham, the founder of Answers in Genesis; and Joe Bastardi, a meteorologist who has argued that carbon dioxide does not contribute to global warming.

Colbert asked Nye if there was a particular scientist whom he might nominate as a national hero. Nye’s answer was Rosalind Franklin, the British scientist whose work led to the discovery of the double-helix shape of DNA. “You’re looking down the barrel at the image of DNA,” Nye said.

“You think you might have a way to persuade President Trump to take climate change seriously. What is it?” Colbert asked, as the audience “oohed.” (A short clip of Trump in the documentary had been met with a loud chorus of boos from the audience.)

“We think we can get to the president through space exploration,” Nye said. For there was evidence, he said, that the president changes his mind on a lot of things. “The EPA was started by Richard Nixon, for crying out loud!” Nye said.

“Richard Nixon could not be elected as a Republican today,” Colbert remarked.

Nye and Colbert also brought up a bit of trivia: Article One, Section Eight of the U.S. Constitution gives Congress the ability “to promote the progress of science and useful arts.” “Like comedy,” Nye said.

“And engineering,” Colbert added.

They also briefly discussed the Solutions Project, an ongoing project to demonstrate how the United States could conceivably run on renewable energy sources. “Did anybody buy a T-shirt?” Nye asked the audience. “It’s not magic, it’s...”

“Science!” the audience finished.

For the final question, Colbert asked if there was any piece of science or technology that Nye was especially amazed about.

“My phone tells me which side of the street I’m on!” Nye exclaimed.