A fine display of shooting stars is underway and peaks overnight Wednesday into early Thursday morning. Astronomers expect the 2004 Perseid meteor shower to be one of the best versions of the annual event in several years.
Watching meteors requires no special gear -- telescopes and binoculars are of no use. So anyone in the Northern Hemisphere with clear skies could see some "shooting stars."
Seasoned meteor watchers suggest finding a dark location away from city and suburban lights, if possible. Some brighter streaks will be visible from cities but urban lighting will drown out the bulk of them. Take a blanket or lounge chair so you can lie back and scan as much of the sky as possible, experts say.
Perseids can appear anywhere in the sky, but if traced back they will appear to emanate from a point in the constellation Perseus, which rises in late evening in the East and is high overhead in the wee hours before sunrise.
When to watch
During peak times, and for moments or perhaps hours at a stretch, the Perseids could generate about a meteor every minute for viewer's in dark locations. Sporadic brief bursts of a few in a single minute sometimes occur.
A good display could begin Wednesday night starting around 9 p.m. local time for those with dark skies. Because of the celestial mechanics involved, a few "earthgrazing" meteors could emerge from near the horizon in these late evening hours and race horizontally across the sky.
The hours from 2 a.m. until dawn local time Thursday will be the best. That is when the side of Earth you stand on faces the oncoming stream of debris that creates the shower. Like an ornament on the hood of a car, a predawn viewer sees bits of ancient comet dust being scooped up by Earth's atmosphere as the planet plunges on its orbital course around the Sun. Nighttime meteors have to catch up to the planet.
As a bonus Thursday, a thin crescent Moon will appear near Venus in the eastern predawn sky. Venus is unmistakably bright, outshining all other stars and planets right now.
Unlike last year when a Full Moon outshone many Perseids, this year the thin Moon won't be much of a hindrance.
Behind the shower
The Perseids are the result of stream of debris in space laid down by comet Swift-Tuttle, which orbits the Sun every 130 years and spends most of its time in the far reaches of the solar system. On each pass inward, bits of dust -- mostly the size of sand grains but sometimes as big as marbles -- boil from the comet's surface. When Earth passes through the debris each August, the bits are vaporized in the atmosphere.
"Expect 40 to 60 meteors per hour, some of them bright," says Bill Cooke, a researcher at NASA's Marshall Space Flight Center.
An even busier shower might await skywatchers in Europe, Africa and Asia. Astronomers predict Earth will pass through a dense portion of the stream at around 4:50 p.m. ET (20:50 GMT) on Wednesday. The Perseids typically do not put on much of a show south of the equator.
The Perseids have been ramping up for about two weeks. The activity will drop off rapidly after Thursday morning but stragglers will appear for up to a week. Other meteors not associated with the Perseids are also visible this time of year.