Whether it comes as a light shower or historic monsoon, tonight's meteor bombardment should dazzle anyone blessed with a clear, dark sky.
But high clouds may deny most Marylanders an unobstructed view of the celestial pyrotechnics.
Just as night falls, the Earth is expected to make its annual pass near the center of the stream of rocky dust and debris tumbling after the comet Swift-Tuttle in its orbit around the sun.
Every August, this debris slams into the atmosphere, incinerates and produces the Perseid meteors, typically the most intense of the meteor showers that occur about once a month.
But this year's Perseids (pronounced PER-see-ids and named after the constellation Perseus) could be different. Two Canadian scientists predict that tonight could bring a rare meteor storm, one of the most intense barrages ever recorded.
Where the Perseids typically fire off about 100 meteors an hour, tonight could bring brief squalls of hundreds of meteors per minute. (Fear of an intense storm prompted NASA to postpone its latest space shuttle flight until tomorrow morning. And NASA plans to spin the Hubble Space Telescope around in orbit today to protect its mirror from stray debris.)
Not everyone sees a meteor storm brewing tonight.
Two London astronomers calculate that a strong shower this year will be followed by an all-out storm next year. David Hughes of the University of Sheffield in England says there is no way to reliably predict the intensity of a meteor shower.
But the mere possibility of a record-setting fusillade of shooting stars has piqued the interest of many astrophysicists, amateur astronomers and casual sky-watchers.
In the mid-Atlantic, the weather could be a problem.
High-flying, wispy cirrus clouds may fill almost half the sky over Baltimore tonight, said Fred Davis of the National Weather Service at Baltimore-Washington International Airport. Some meteors may be obscured while many others may appear to be falling behind a gauze curtain.
Dense cloud cover, meanwhile, is forecast for the northern fringe of Maryland and most of Pennsylvania. If those clouds drift south, that will cancel the 1993 Perseids show here.
If the weather cooperates, here's how to watch:
Meteors should be visible between about 9 p.m. and the start of morning twilight tomorrow. The best time for viewing should be between 11 p.m. and 1 a.m., after the skies grow dark and before the moon rises. (The storm can come, if it comes, at any time.)
Astronomers say the best viewing is done in a lawn chair. But don't get too comfortable. You may snooze through the storm of the century. And don't worry about getting hit. Most meteors could fit through the holes of a salt-shaker, and they vaporize before they get anywhere near the Earth's surface.
Look in the general direction of northeast, toward the constellation Perseus. (Telescopes and binoculars limit your field view. Don't use them.)
Viewing is best in an open field far from city and street lights, with as wide a horizon as you can find. Let your eyes adjust to the dark. Sip on some iced tea and relax. This isn't rocket science.
Stephen P. Maran, an astronomer and spokesman for the American Astronomical Society, plans to join a group of star-gazing friends on a field trip that could take them as far away as New Jersey tonight, in pursuit of clear skies.
"I think we'll see some good meteors," said Dr. Maran, who is taking a couple of day's leave from NASA's Goddard Space Flight Center in Greenbelt to chase the Perseids. "Whether it's a great shower or not may be in the eyes of the beholder."
Comets are made of ice covered with a rocky grit. As a comet approaches the Sun during its long orbit, its surface heats up and evaporates, carrying off sandy debris in clouds and explosive jets.
This debris traces about the same orbital path as the comet, traveling a little faster or slower. Over thousands of years, the comet's entire orbital path is filled with high-velocity gravel.
Paul D. Feldman, professor of physics and astronomy at the Johns Hopkins University, said Swift-Tuttle, which orbits the Sun once every 130 years or so, sloughs off an unusually large amount of rubble. So the potential, at least, for a big storm is there.