Bill Nye the Science Guy is back for a second season of "Bill Nye Saves the World," which returns to Netflix today (Dec. 29).

The new season kicks off at a cannabis dispensary in Hollywood, where Nye examines the science behind marijuana, a Schedule I drug in the U.S. that is "presumed to have no medical value and be addictive," Nye told Space.com. 

Even though marijuana is widely used for medical purposes, it has not been legalized everywhere in the U.S., and "nobody really knows for sure" what the active chemical components of the drug do, Nye said. That's why Nye legally purchases a sample from the cannabis dispensary to learn more about the controversial plant. 

Other episodes of the new season delve into topics like cybersecurity, extinction, sleep, superbugs and even time travel, Nye said.

Joined by actor Zach Braff, retired astronaut Scott Kelly, and Brannon Braga, a producer who has worked on "Star Trek," "Cosmos: A Spacetime Odyssey" and "The Orville," Nye breaks down the science of time travel and provides "an update on our current understanding of the astrophysics" of time travel, he told Space.com.  

Bill Nye the Science Guy returns to Netflix Friday, Dec. 29, for Season 2 of his show "Bill Nye Saves the World."
Bill Nye the Science Guy returns to Netflix Friday, Dec. 29, for Season 2 of his show "Bill Nye Saves the World."
Credit: Netflix

The second season of "Bill Nye Saves the World" will feature many other famous guests, including actors Kevin Smith, Steve-O and Drew Carey, as well as comedian Ali Wong and musicians from the band OK Go. 

Nye also turns to NASA experts to better understand sleep patterns of humans on Earth, as well as astronauts at the International Space Station, who see the sun rise and set about once every 90 minutes. 

"It makes you a little disoriented, by all accounts," which is why NASA scientists strive to better understand sleep, Nye told Space.com. 

This also relates to the question of how astronauts would get a good night's sleep during future missions to Mars, where the day is about 40 minutes longer than a day on Earth. "Could you do that — live on a Martian day, or would it make you nuts because you're hardwired for an Earth day?" Nye said. 

Only the first six episodes of "Bill Nye Saves the World" will be released today, Dec. 29, on Netflix, which requires a monthly paid subscription. The remaining six episodes will follow sometime in 2018. The original 1990s kids' TV show "Bill Nye, the Science Guy" is also available to stream on Netflix.

Follow Samantha Mathewson @Sam_Ashley13. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.