Why do cats purr? How a science teacher went viral

The science of lying. The terrifying truth about bananas. The teenage brain explained.

These are just a few of the subjects that musician and entrepreneur Hank Green has tackled in YouTube videos that have helped him win a huge online following and made him one of the country’s better-known science teachers.

“I’m Hank Green and I want to teach you chemistry. Please, do not run away screaming,” he says, beginning a 10-minute video about atoms that has been viewed 1.6 million times.

“Chemistry is not torture but instead the amazing and beautiful science of stuff, and if you give it a chance, it will not only blow your mind but also give you a deeper understanding of your world.”

The videos aren’t fancy. The set is basic, the animation simple.

They are mostly Green in his dark-rimmed glasses and button-down shirts, talking quickly, dropping jokes and turning science into an irresistible story.

“He really seems to thrive off the sharing of this learning. There is so much out there that we don’t know, and science is just barely scraping the tip of the iceberg,” said Mary Dalton, a tutor in Glendora, Calif., who this summer used videos from Green’s SciShow YouTube channel with her fifth- and sixth-grade students.

“My kids asked for SciShow homework every day,” she said. “When you have kids asking for homework, you know you have something special.”

Green stumbled into Internet sensation-dom by way of a project with his brother John Green, the bestselling author of The Fault in Our Stars.

In 2006, they resolved to forgo writing to each other for a year and communicate instead by videos in which they talked about whatever came to mind, from their latest vacations to Harry Potter.

They became known as Vlogbrothers, their fans as Nerdfighters.

At some point, however, they ran out of things to talk about.

So they started explaining stuff. And their YouTube channels emerged, including SciShow, a pop-science exploration of everyday phenomena (Why do cats purr?).

Another channel is CrashCourse, a series of videos by the Green brothers delving into the basics of history and science, from the colonization of America to the Big Bang Theory and the digestive system.

CrashCourse has become a popular tool for American high school teachers and students: During winter break, viewership plummets, Hank Green said. And it skyrockets just before Advanced Placement exams, when students are studying.

Online, commenters sometimes wonder why science class can’t be more like Hank Green’s science videos: entertaining, and fascinating.

Green said in an interview that he has the advantage of being able to edit himself, and he hopes the videos are a useful tool for teachers in the classroom.

“Teachers are asked to do so much, and they can’t be good at every single thing,” he said.

“My goal is to be good at one thing so teachers can be good at other things.”

The Green brothers’ YouTube channels and their hundreds of original videos have attracted nearly eight million subscribers and fetched nearly one billion views.

It’s a following large enough to have captured the attention of the White House; Hank Green was among a handful of YouTube stars invited to interview President Barack Obama in January.

Green said he was the kind of kid who saw high school as a game, where the winner got the best grades with the least effort.

But he said his chemistry teacher inspired him to work harder and dig into tough problems.

He said he hopes his work helps persuade young people to do the same.

“I want smart people to be solving all the hard problems to solve in the next 50 to 100 years,” Green said.

“I just want people to be excited about hard stuff, that’s what engineering is.”

"Chemistry is not torture," science teacher Hank Green promises.