Sky watchers could catch a dazzling treat on Tuesday and Wednesday, with the peak of the annual Perseid meteor shower.
Meteors are bits of dust or rock that collide with Earth's atmosphere and heat up gas particles to produce a glowing trail. A handful of meteors can be seen each hour on any clear night, but during a meteor shower dozens may be visible.
The Perseid shower occurs each year when the Earth passes through a stream of debris shed by the comet Swift-Tuttle, which orbits the sun once every 130 years or so and last passed through the inner solar system in 1992.
The Perseid shower is expected to reach its peak at 1:30 p.m. on August 12, but dozens of meteors per hour should be visible on the nights preceding and following the peak. The best time to catch the shower may be around 4:00 a.m. on August 12, when meteor numbers may get a slight boost as the Earth passes by an additional stream of debris left by the comet in 1610.
On a clear night, an average of 60 meteors can be seen per hour close to the Perseids' peak. This year, the number may be lower because the moon, which is approaching its last quarter, will rise at about the same time as the shower is expected to begin.
Moonshine could obscure the fainter meteors, cutting the total number of meteors that might be seen in half, says Tony Cook of the Griffith Observatory in Los Angeles. "That actually might bother meteor experts more than it does people who want to enjoy the shower, because the ones you want to see are the really bright ones anyway," Cook says.
The Perseid meteor shower gets its name because the meteor trails all lead back to a point in the northern constellation Perseus.
Every evening this week, the shower should start around 11 p.m. local time as the Perseus constellation rises, and the number of visible meteors should increase as the evening progresses to peak before dawn.
Perseid Meteor Shower 2009
The meteors will appear all over the sky, so the best strategy for viewing the shower is to lie down and stare at as large a patch of sky as possible. Observers will want to point their gaze away from the moon to reduce its effect on night vision.
Although the best Perseid viewing is in the northern hemisphere, some viewers just south of the equator may also be able to catch a glimpse.