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Science & Space

Summer meteor showers descend

By Joe Rao
SPACE.comexternal link

A photograph taken from Colorado Mountain College in Steamboat Springs.
A photograph taken from Colorado Mountain College in Steamboat Springs.
Meteor shower

( -- Summer is the season for shooting stars, and this year could be among the best as the annual Perseid meteor shower promises to be better than usual.

Anyone gazing at the summer night sky for even a short length of time now through the end of August is likely to spot a few streaks of otherworldly light. In general, the Earth encounters richer meteoric activity during the second half of the year.

The best meteor display of the summer comes during the second week of August, during the Perseid event. At its peak around the nights of Aug. 11 and 12, the shower can produce 50 to 100 fast, bright meteors per hour for any observer with a wide-open view of a dark sky.

Great prospects

This year will be an excellent one to watch for the Perseids, partly because bright moonlight will not interfere as in past years, and also because Earth might encounter a heavier concentration of meteoric debris, astronomers predict, leading to better than normal meteor activity.

Perseid meteors are bits of debris -- typically no larger than sand grains but sometimes up to marble size -- left behind during repeated passes of comet Swift-Tuttle. The comet crosses the inner solar system once every 128 years as part of its elongated orbit around the Sun.

Because most meteors in a shower are tiny, there is little threat to spacecraft, and virtually none to people on the ground.

Forerunners of the Perseid shower began to appear around July 17. Try watching for them after the waxing moon has left the sky, leaving the predawn hours dark. You'll see only a few per hour at best, but the numbers will begin to ramp-up during the second week of August.

At the height of the event, you might spot one to two per minute, and sometimes even more meteors can grace the sky during brief bursts.

The last Perseid stragglers may still be spotted as late as Aug. 24.

Other meteors

To go along with the Perseids, there are at least ten other minor meteor displays that are active at various times during July and August. While the hourly rates from these other streams are but a fraction of the numbers produced by the Perseids, overall they provide a wide variety of meteors of differing colors, speeds and paths.

Among these are the Southern Delta Aquarids, which can produce faint, medium speed meteors; the Alpha Capricornids, described as slow, bright, long trailed meteors, and the Kappa Cygnids, which are classified as slow-moving and sometimes brilliantly lit.

Summertime meteors, occasionally flitting across your line of sight, are especially noticeable between mid-July and the third week of August. Six of the minor displays occur between Aug. 3 and 15.

The only equipment you'll need are your eyes and a modest amount of patience. Find a location away from bright lights and with a wide view of the sky. Bring a blanket or lounge chair so you can relax while looking up.

When to watch

Early morning hours generally provide the best viewing, typically offering up twice as many meteors as in the evening. Why?

In the predawn, you're standing like a hood ornament on the side of Earth facing the oncoming traffic, as compared to the evening hours when you're on the trailing edge of the planet's orbital plunge through around the sun.

Evening meteors much catch Earth by having an orbital velocity greater than the planet. After midnight, any particle in the planet's path is scooped up in the atmosphere, slamming into the air at speeds of 7 to 45 miles per second (11-72 kps). Their energy of motion rapidly dissipates in the form of heat, light, and ionization, creating short-lived streaks of light.

On Aug. 6, will publish a comprehensive viewer's guide for the Perseid meteor shower.

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