2010 RF12 and another small asteroid that passed close to earth Wednesday were detected three days before their fly-by, illustrating the improving capability of asteroid-spotting telescopes.
In an unprecedented event, two asteroids will pass our planet Wednesday at a distance closer than the moon. Neither rock threatens to strike the earth, say astronomers.
With dedication and good timing, amateur astronomers have helped track asteroids and search for planets. NASA is enlisting some for a moon observation mission.