Let’s call today freaky space rock Friday. As Will Englund reports from Russia, a fireball zoomed across the sky near Chelyabinsk in the Ural Mountains around 9:20 a.m. local time, shattering glass, injuring more than 900 and sending 43 people to the hospital, according to health officials.

Meanwhile, an asteroid known as 2012 DA14 will zoom past Earth this afternoon -- but at a safe distance.

The object that caused the Russian fireball was either a small asteroid or a chunk of a comet. When such space rocks hit the atmosphere, they  become known as meteors. Any meteor fragments that reach the ground are then called meteorites.

Meteor showers occur when the Earth passes through loose fields of debris from comets and thousands of fragments -- from paint-chip sized flecks up to boulder-sized pieces or bigger -- penetrate the atmosphere, setting off sometimes spectacular sky shows. These showers, such as the Perseids and Leonids, occur at regular times of the year as the Earth swings through these debris fields.

- Brian Vastag