Stu Megan, a semi-retired computer specialist, reviews online images for the University of Arizona's Spacewatch program. He has pored over more than 6,500 images since the project went public in October.
The program allows volunteers to spot fast-moving space objects, or FMOs, by logging onto a Web site and downloading images taken by telescopes at Kitt Peak National Observatory, 56 miles southwest of Tucson.
Megan spotted the asteroid - now known as 2004 BV18 - earlier this month. It is the first one discovered by a Spacewatch volunteer to be confirmed by the Minor Planet Center, the official body that deals with such observations.
"I think it's really cool," Megan said. "I've got all this time to spare. Plus, I can multi-task. I've got two computers."
The asteroid missed the Earth by 1.2 million miles, but it wouldn't have done much more than offer a pretty light show even if it had been aimed directly at us, said Robert McMillan, who directs Spacewatch. At an estimated size of 60 feet by 120 feet, the asteroid would have burned up as it coursed through Earth's upper atmosphere, he said.
Spacewatch primarily studies the movement of asteroids and comets. Volunteers fill an important niche, McMillan said, while researchers at the University of Arizona and automated computers track larger objects in space.
One of the program's major goals is to search for objects that could become potential destinations for spacecraft missions, while another lies in identifying asteroids larger than a kilometer in diameter heading toward Earth.
An impact by an asteroid that size could cause a global catastrophe.