A night of shooting stars

Thousands of people in North America who got up early on Nov. 18 were dazzled by a memorable sky show. White, yellow, blue, and green fireballs, some leaving behind smoke trails, streaked across the sky.

Sequence of images shows the evolution of a single Leonid fireball. D. Mammana

For sky watchers in the United States, it was probably the best Leonid meteor shower since the 1966 storm and is unlikely to be matched for another 3 decades. As several teams of researchers had predicted, residents of eastern Asia and Australia were treated to a veritable storm, with several thousand meteors an hour illuminating the sky (SN: 11/10/01, p. 293: Meteor shower promises quite a show).

The Leonid shower happens every November, when Earth plows through bands of dusty debris, or meteoroids, shed over the centuries by Comet 55P/Tempel-Tuttle. The meteoroids burn up in Earth’s atmosphere, creating the spectacle.

According to a Nov. 19 circular of the International Astronomical Union, the shower had two peaks. The first occurred about 5:30 a.m. EST, when Earth intercepted a meteoroid stream that astronomers believe the comet ejected in 1767. This peak produced about 800 meteors an hour. However, North Americans near the bright lights of major cities probably saw no more than 100 an hour, says Brian G. Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

The other, much higher peak of several thousand meteors per hour occurred around 4:30 a.m. Japan Standard Time on Nov. 19, when Earth plowed through a debris stream left behind in 1866.

Both peaks occurred about half an hour later than some researchers had calculated, but “I think the predictions fared very well indeed,” says Marsden. “This year was the first real test of the [debris]-trail model,” he says. That model assumes that the dust expelled by Tempel-Tuttle each time it nears the sun forms a separate stream of debris that remains relatively narrow for centuries.

During the Leonid shower, several observers reported flashes of light from the moon. Because the moon has no atmosphere, meteoroids strike the lunar surface instead of disintegrating. Most of the dusty debris is composed of tiny particles, but the ones that generated the lunar explosions visible from Earth could have been as heavy as 10 kilograms, researchers estimate.

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