How common are fireballs streaking across the sky?

Rocks from outer space are constantly hurtling toward Earth, slamming into the atmosphere and often exploding into fireballs that both delight and alarm people. Thankfully, the vast majority cause no damage because they are smashed into small chunks or dust. A fireball streaked across the sky near Cleveland this week, caused by what was thought to be a space rock weighing 7 tons. The American Meteor Society says it was seen from Wisconsin to Maryland. No fragments have been found yet.