The annual Perseid meteor shower - one of the year's most-watched night-sky events - will be dimmed some by a 72-percent-illuminated moon tonight. When skies are clear, the shower is always worth a few hours of sky-watching on a pleasant summer night. But unfortunately, the forecast tonight is not too promising, either.

The Perseids occur each summer as the Earth, making its way around the sun on its annual trek, passes through the broad dust trail left behind by Comet Swift-Tuttle. Although the peak of the shower occurs on the night of Aug. 11-12, the rate at which the dust particles strike the Earth's atmosphere (think of bugs smacking into your windshield) has been rising for weeks, and will take weeks to settle down again to background levels.

Astronomers say we will be slicing through a denser-than-normal patch of the dust trail tonight, with meteor rates as high as 200 per hour possible for short periods of time. But these things are notoriously fickle. Here is a gallery of some of last summer's Perseids.

Given the moonrise at around 10:30 p.m., meteor watchers would be well-advised to get outside to a dark location after sunset. The best time might be between 9 and 11 p.m. After that, we'll have to stand with our backs to the moon and take whatever we can get in the moonlight. The dimmest meteors will be washed out, but bright ones should break through.

The best time to watch, if there were no moon, would normally be in the hours before dawn Wednesday morning. 

All that's needed to spot meteors are a dark location, as far from urban lighting as you can get; a comfortable place to stretch out - a beach lounger, a blanket or sleeping bag - and a broad stretch of sky. Although the meteors will appear to radiate from the constellation Perseus, in the northeast before midnight, you should be able to spot them anywhere in the sky. Evening hours will be best for catching "Earth-grazers" as they skim across the sky at the top of the atmosphere, like stones skipping across a pond.

If clouds cancel the party, try again any night this week. Rates will be diminished, but a night out under the stars, with whatever meteors occur, is always worthwhile. Jupiter is brilliant in the southeast in late evening; the moon, Mars and Venus rise and follow the giant planet into the sky  by 3 a.m.

(SUN PHOTO/Karl Merton Ferron/August 2007)