Brew some coffee. Unpack the lawn chairs. Astronomers predict this year's Leonids meteor display, expected to appear before dawn Sunday, will be a dazzler worth missing a little sleep.
''It's now or never,'' said Robert Naeye of the Astronomy Society of the Pacific. ''Astronomers don't think we'll see another storm like this one until the year 2099. We will probably never see a better meteor shower in our lifetimes.''
Every year scientists fly to places like the Gobi Desert or Canary Islands to watch the heavens rain fire for a few minutes in November. This year, Earth's alignment suggests that North America will be squarely beneath some of the most vigorous shooting stars. Pacific Islands and the Far East may see natural fireworks, too.
The most optimistic celestial forecasts call for a steady storm of 4,000 meteors per hour, or about 70 per minute around 5 a.m. EST Sunday. With clear skies, luck and the bonus of a nearly moonless night, people in some locations could see twice that.
The Leonids are dust particles shed by Comet Tempel-Tuttle. Like a truck barreling down a dirt road, the comet trails a cloud of dust as it orbits the sun once every 33 years.
The meteors are called Leonids because they appear to radiate from the constellation Leo, the Lion. A really big meteor is equal to a grain of rice.
Earth usually crosses a thin section of the Leonids trail; perhaps 10 meteors per hour streak across the night sky.
When the comet sweeps close to the sun, the sun's heat causes it to shed more debris like a truck hitting a mud puddle. Earth gets splattered when it plows though the thick wake. It occurs every November for a few years until the particles dissipate.
In 1966, observers couldn't count the shooting stars fast enough. Estimates ranged as high as 150,000 per hour.
Comet Tempel-Tuttle most recently orbited the sun in February 1998, and since then, in the words of forecaster Joe Rao, the Leonids have ''gone berserk.''
While meteor displays thrill amateur stargazers, they also hold scientific promise. Comets are hurtling balls of ice and debris left over from the birth of the solar system more than 4 billion years ago.
The particles contain basic elements like iron, as well as carbon-based molecules. Some scientists believe this is how Earth was seeded with organic compounds.
''The chemical precursors to life -- found in comet dust -- may well have survived a plunge into early Earth's atmosphere,'' said NASA scientist Peter Jenniskens, who directs airborne surveys of the Leonids.
Earthbound viewers are safe during a meteor shower because the tiny particles tend to burn 15 miles from Earth. In fact, the visible meteor actually is the streak of light caused by the particle, or meteoroid, that is generating friction against the atmosphere.
But in space, the tiniest debris behaves like a speeding bullet. Satellite operators are turning their orbiting equipment edge-on into the storm so delicate sensors and solar energy arrays will not be crippled by the barrage.
Predicting the Leonids' vigor has become an annual competition. Previously educated guesswork meteor predictions are now the products of sophisticated computer models, enabling scientists to nail the storm peaks within a few minutes. This year, the Earth will pass through multiple debris trails shed by the comet as long ago as 1699.
''The comet is almost 4 years behind us now,'' said Rao, who handicaps the Leonids for Sky & Telescope magazine and the American Museum of Natural History in New York. ''The predictions are all over the place.''
Tom Van Flandern of Meta Research in Chevy Chase, Md., a non-profit astronomy group, predicts ''no fewer than five streams will pass close to the Earth, so that weak (meteor) storms may persist for several hours before the predicted strong one arrives.''
How strong? Jenniskens is the most optimistic forecaster. He predicts the Leonids will peak at 4,200 per hour at 5:09 a.m. Sunday over the East Coast, 2:09 a.m. over the West Coast. Others predict a peak of 1,300 to 2,000 per hour.
Predictions elsewhere vary as widely. One group expects a bigger storm eight hours later over the Far East; William Cooke of NASA's Marshall Space Flight Center predicts no more than 800 meteors per hour over the Far East.
With so much uncertainty, most U.S. meteor chasers have decided to stay home this year. Circumstances following the Sept. 11 terrorist attacks have affected some plans; airspace restrictions probably will ground Jenniskens' airborne mission.
Naeye is joining an astronomers gathering at the Kitt Peak observatory in southern Arizona, where the skies should be dark and the weather dry.
''The U.S. will get a pretty good show,'' Naeye said. ''Everything is lining up just right.''
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