Bad Timing Dims Prospects for Comet Show : Space: The Perseid shower may produce hundreds of meteors per hour. But don’t expect to see much here--the event will peak hours before sunset.

Dusty flakes from a speeding comet may provide one of the most spectacular meteor shows in a generation Wednesday, but astronomers are restraining their enthusiasm to avoid overselling the event--particularly on the West Coast, where the event will peak hours before sunset.

The phenomenon is the annual Perseid meteor shower, a burst of shooting stars that normally can be counted on to produce a heavenly flash about once a minute for the better part of a night. This year, however, conditions are such that some astronomers expect a brilliant storm of perhaps hundreds of meteors per hour.

Although the celestial fireworks show should peak at 6 p.m. Pacific time on Wednesday, astronomer Brian G. Marsden of the Harvard-Smithsonian Astronomical Observatory said a few shooting stars may be visible after dusk in California.

With the three-hour time difference, the eastern United States will see more of the shower. The best viewing will be early Thursday morning in Europe and the Middle East.

“How good a show will it be? It’s anyone’s guess, really,” Marsden said. “There is a good chance of a spectacular shower, maybe even a storm. But we really don’t understand the process all that well, so it’s hard to predict with any degree of accuracy.”

One of the hardest factors to predict, he said, is weather. Forecasts call for intermittent clouds and fog Wednesday night in Southern California basins and deserts.

The best viewing will be far from the city, where glare from street lights and signs tends to wash out most astronomical events. The meteors should appear to emerge from the constellation Perseus, just above the horizon in the north-northeast section of the sky.

Meteors are caused when asteroids or other bits of interplanetary flotsam slam into Earth’s atmosphere and are incinerated by friction. The Perseid shower occurs when Earth encounters dust sloughed off a dirty ball of ice called Comet Swift-Tuttle.

Over the eons, Swift-Tuttle has left a ring of dust along the length of its eccentric 130-year orbit through the solar system. This assures a meteor shower of some sort each August as Earth comes close to intersecting that orbit.

Astronomers anticipate a flashier-than-usual Perseid show this year because Earth will pass exceptionally close to Swift-Tuttle’s orbit--within 90,000 miles, a mere hairsbreadth in cosmic scales.

“It’s the 90,000-mile number that makes us think we might be in for a good show,” Marsden said.

Last fall, the comet itself made its closest approach to Earth since 1863. This raised hope that Swift-Tuttle might have replenished the meteor-making dust in its orbit. Dust from Swift-Tuttle generally screams into Earth’s atmosphere at 134,000 m.p.h. and burns up 40 to 60 miles above sea level.

The National Aeronautics and Space Administration inadvertently spurred interest in the Perseid meteor shower last week when it announced that it would postpone the launch of the space shuttle Discovery and close the aperture door on the Hubble Space Telescope to protect them from the remote chance of damage from comet dust.

If the meteor shower lives up to expectations, it could be the first storm seen from Earth since the spectacular Leonid storm of November, 1966. In that storm, which peaked over the western United States, some astronomers reported seeing 150,000 meteors per hour.

If this year’s event turns out to be less than spectacular, history shows that the Perseid shower may redeem itself next year. The aftermath of a close passage is sometimes not visible until 18 months after comets have sped past Earth, Marsden said.

That would work to the advantage of West Coast astronomers. The Perseid shower should peak near midnight over California next year.

Night of the Shooting Stars

Observers in the United States, Europe and western Asia may see an unusually impressive Perseid meteor shower this year. The star chart above shows the view about 10 p.m. Pacific timeWednesday.

What are meteors?: They are fast-moving streaks of light visible for a few seconds. They are caused by fragments of rock or metal burning up as they flash through the Earth’s atmosphere. Annual meteor showers happen because the Earth crosses the fragment’s orbit at the same time each year. Debrius from comet Swift-Tuttle is source of Perseid shower Source: Sky & Telescope magazine