Meteor tracks: first fireball videos.

Brighter than the full moon, the greenish white fireball streaked across West Virginia, then raced northeast more than 700 kilometers before dropping at least one rocky chunk in Peekskill, N.Y Celestial light shows like this are far from unique. But the event observed on Oct. 9, 1992, came at an auspicious time: a Friday evening when many people were outdoors watching high school football games. Instead of videotaping touchdowns, several recorded the rough-and-tumble action overhead.

Fireballs are generated when a meteoroid, a rocky body from outer space, burns up in Earth's atmosphere. The 14 videos examined by researchers represent the first known motion pictures to document the passage of a meteoroid that has dropped a fragment of its rocky body to Earth. "It's the first time we can actually see, at one-thirtieth of a second intervals, how a fireball passes through the atmosphere," says George W. Wetherill of the Carnegie Institution of Washington in Washington, D.C.

He and his colleagues, including Robert L. Hawkes of Mount Allison University in Sackville, New Brunswick, and Peter Brown of the University of Western Ontario in London, Ontario, detail their analysis of the tapes and still images in the Feb. 17 NATURE.

Wetherill says the videotapes offer astronomers a valuable set of finger-prints. The tapes can help identify which fireballs, among thousands recorded by still cameras worldwide, are generated by meteoroids that don't completely disintegrate. The remains fall to the ground as meteorites. Although people have photographed three other fireballs from which meteorites have been recovered, no telltale time sequence exists for these events, he adds.

Because the Oct. 9 fireball entered the atmosphere at a grazing angle, it lasted long enough for people in several states to videotape it for as long as 22 seconds, Hawkes says. The origin of the parent meteoroid remains unknown, he notes, but the roughly 20-ton body never strayed farther from the sun than the asteroid belt's inner edge, about double the distance between Earth and the sun. The videos show that the luminosity of the meteoroid flickered about six times a second before fragmenting. Rotation of the meteoroid could have caused the flickering, Brown says. Alternatively, he notes, it might have stemmed from molten rock periodically dripping off the burning body.