How confident are scientists that world won't end on December 21? Here's a Neil deGrasse Tyson tweet from several weeks ago:

Tyson is not alone. NASA scientists are also so confident, in fact, that they released a video explaining why the world "didn't end yesterday" 10 days in advance. In the video below, we hear from Dr. John Carlson, director of the Center for Archaeoastronomy, who says the Mayan calendar actually did not end on December 21 and the Mayans never predicted that date would be the end of the world. 

NASA astrobiologist David Morrison also echoes Tyson: "If there were anything out there like a planet heading for earth, it would already be one of the brightest objects in the sky. Everybody on earth (would be able) to see it.

Watch the video here: