1999 Leonids coverage Viewing Tips A Dark, Stormy Night Audio Feature

by Damond Benningfield

Hubble Space Telescope rarely misses a chance to watch a heavenly spectacle. But on November 16 and 17, while stargazers on Earth watch the Leonid meteor shower — and hope for a meteor storm — the orbiting observatory will point anywhere except at the constellation Leo, where the meteor shower originates. Scientists fear the particles that cause the Leonids could damage HST's mirror or sensitive electronics.

The Leonid shower occurs every November as Earth sweeps through the orbit of Comet Tempel-Tuttle. Most years, the Leonids produce no more than a few dozen meteors an hour at their peak. But every 33 years, when the comet approaches the Sun, there is a chance that the Leonids could produce a spectacular storm, with a peak rate of thousands of "shooting stars" an hour.

The Leonids have produced some of the most spectacular meteor storms in history. In 1833, Americans were awakened by a shower so intense that the sky seemed to be on fire; some thought the shower heralded the end of the world. The last storm occurred in 1966, when observers in the western United States estimated that as many as 40 meteors streaked across the sky every second.

Tempel-Tuttle returned to the inner solar system this year, releasing countless bits of rock and dirt as it passed near the Sun. The comet dust is spread out all along Tempel-Tuttle's orbit, but it is most dense near the comet. When Earth passes through the debris, grains of comet dust streak at high speed into our atmosphere and vaporize as bright streaks of light. There are more dust grains close to the comet, so we see more meteors around the time when Tempel-Tuttle passes near the Sun.

That's great news for skywatchers, but bad news for satellite operators.

Most of the particles that produce Leonid meteors are no larger than grains of sand. But some are the size of BBs or marbles, or even bigger. If such large particles hit an orbiting spacecraft, they could damage or even destroy the craft. A Perseid meteor may have knocked out a communications satellite in 1992. Even the smallest particles can produce clouds of electrically charged atoms when they strike a satellite, short-circuiting computers or other electronic systems.

Most years, meteor showers are not much of a threat. But when the number of particles increases a thousandfold, scientists and engineers pay attention.

Hubble Space Telescope will keep working, but will turn away from the meteor stream. Space shuttles will be grounded during the storm. Intelsat, which operates several communication satellites, will turn the satellites so their solar panels face away from the meteors, and will station extra engineers in their control rooms to handle any problems that occur. Many other scientific, military, and commercial satellites will close protective shutters, shut down key systems, or take other precautions.

From the safety of Earth's surface, though, the Leonids provide a good excuse for getting outside to watch the stars. The best times for Leonid meteors are the nights of November 16 and 17. Look after midnight, when the constellation Leo rises above the east-northeastern horizon. Leonid meteors can appear anywhere in the sky, although their paths appear to enter Earth's atmosphere from the direction of Leo.

Peak rates in the United States probably will not exceed a few dozen meteors an hour. (Hawaii will get the best view, with perhaps a hundred meteors an hour before dawn on the 17th.) The Moon will be new on the 18th, so it will not interfere with the fireworks.

For the best view of the Leonids, travel to eastern Asia, where the shower could produce peak rates of several thousand meteors an hour. No one knows for sure, though; meteor showers are notoriously tricky to predict.

If you miss this year's Leonids, try again next year. Although there will be more nighttime moonlight, some scientists say the Leonids could storm again in 1999 — producing more fireworks in the night sky, and more headaches for satellite operators.

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