Dodging a Bullet 
In the "Stargate: SG1" TV series, a bad guy known as Apophis kept taking shots at Earth and its heroes, but he always missed. Fortunately for us, an asteroid named Apophis won't have any more luck -- at least for quite a while.
Apophis was discovered six years ago as part of a search for asteroids that might one day threaten Earth. It's more than twice the length of a football field -- big enough to cause significant damage if it hit us.
And early calculations showed that it might do just that in 2029. Because of the threat, the astronomers who discovered the asteroid named it after the character from SG1. As they tracked the asteroid and learned more about its orbit, though, scientists determined that Apophis will miss us by about 20,000 miles.
That scary close encounter raised a new concern: that Earth might fling Apophis into just the right orbit to set up a collision in 2036. Last year, though, new data and a more precise plot of its orbit reduced the odds of a collision to about one in a quarter-million.
That plot did reveal a new threat, though -- about a one-in-300,000 chance of a collision in 2068. Astronomers expect that continued tracking will reduce those odds, too. Even so, the asteroid's orbit will continue to periodically bring it close to Earth. So like the heroes of SG1, we'll have to keep a close eye on this cosmic menace.
Tomorrow: a double sunrise on a planetary neighbor.
Script by Damond Benningfield, Copyright 2009