Twenty years ago this fall, Bill Nye came into homes across the U.S. with his TV show, "Bill Nye the Science Guy," and struck a chord with curious children.

There were segments on volcanoes, the science behind the human heart and even why people cry from onions.

To celebrate two decades of teaching children science, Nye released a free app by Disney via iTunes. Disney is the parent company of ABC News.

Image credit: ABC News

"When I talk to the camera, I do my best to talk to one person," he told ABC News. "I'm talking to that kid I want to influence. I want him or her to get excited about this thing that I'm am so excited about: 'Look at this. The boat displaces water that weighs exactly as it does! What is cooler than that? Come on!'"

At Lehigh University's graduation ceremony this spring, students rushed to hug Nye, the commencement speaker, before heading to their parents.

Nye said he, in fact, had been inspired by his mother and father.

His mom had a doctoral degree and was recruited by the U.S. Navy to work as a code breaker on a project so secret she did not talk about it until it was declassified in 1992.

His dad was a prisoner of war held by the Japanese in World War II. He spent four years as a captive and Nye said he created a sundial to help him keep track of time while in prison.

"He would take the shovel handle and cast a shadow with it," Nye said. "Then they would look at the progress of the shadow and he was able to reckon time. He became quite the astronomer, telling 50 constellations without any trouble at all. And so, he brought back these interesting sundials with him, and it affected me in a way I could just really get."

Nye went to Cornell and later worked as an engineer for Boeing before becoming the "science guy."

At Lehigh's commencement, he asked to shake the hand of each graduate - all 1,889 of them.

Nye's challenge for the students: "As I say to everybody, I don't think they are going to remember what I said, but they will remember how they felt, how they feel at that time, and that is very important. … Everybody can make the world better."