Have you ever stepped outside after dinner to walk the dog--just in time to see a bright fireball streak across the sky? It makes you wonder, how often does that happen?

Pretty often, according to astronomer Bill Cooke of the Marshall Space Flight Center. Using a computer model of Earth's meteoroid environment, he made this plot showing the global number of fireballs per day vs. the brightness of the fireball:

According to his calculations, fireballs as bright as Venus appear somewhere on Earth more than 100 times daily. Fireballs as bright as a quarter Moon occur once every ten days, and fireballs as bright as a full Moon once every five months.

The vast majority are never noticed. About 70% of all fireballs streak over uninhabited ocean. Half appear during the day, invisible in sunny skies. Many are missed, however, simply because no one bothers to look up. So grab a leash and a dog (optional), and head outside. The chance of a fireball is better than you think.