De Perseïdenzwerm komt er weer aan

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Put out the lawn chair, set the alarm and maybe bring something to wet your whistle while you gaze into the nighttime sky — the year's best shooting star show has started.

August's annual Perseids meteor shower peaks Sunday and Monday, promising perhaps 70 meteors an hour those evenings.

"The Perseids are the good ones," says meteorite expert Bill Cooke of NASA's Marshall Space Flight Center in Huntsville, Ala.

The Perseids take their name from their apparent origin in the constellation Perseus, the hero of ancient Greek myth born from a shower of heavenly gold. Known for producing fireballs that might streak across a third of the sky, they owe their brilliance to the speed — nearly 134,000 mph — with which they smack into the upper atmosphere. "It's also because of the size of the meteors," Cooke says. The dust grains are about one-fifth of an inch across and burn nicely as they zip overhead.

Those dust grains come courtesy of Comet Swift-Tuttle, which circles the sun once every 133 years and leaves behind a debris trail. (Comets are basically dirty snowballs that develop tails when they approach the sun and start to melt. Different ones are responsible for other regular meteor showers, such as April's Lyrids, brought by Comet C/1861 G1 Thatcher, and November's Leonids brought by Comet 55P/Tempel-Tuttle.)

You will have to stay up late to see the Perseids at their peak; the best viewing comes from midnight to dawn, particularly after the half-full moon sets at 1 a.m. on Monday, says Astronomy magazine's Michael Bakich. But they should appear at night during the week before and after the peak as well.

"Get out of the city and the lights to give yourself a chance to see them," Bakich says. The rule of thumb is that you should be able to see all the stars of the Big Dipper — seven stars if you are counting — to give yourself enough darkness to catch the shooting stars. And give your eyes an hour to adjust.

"There will be a dozen 'ooh' moments in that hour," Bakich says. "Ones when everyone will say, 'Did you see that?'"

Although the shooting stars seem to come from the constellation Perseus, don't look there to see them, Bakich advises. Instead, look about one-third of the sky down and away from the constellation to spot meteors streaking across the sky. "That makes them easier to pick out," he says.

While you are enjoying the sky show, satellite operators are buttoning up spacecraft to protect them from the onslaught of comet dust, says Cooke, who prepares meteor shower forecasts each year for space businesses. While the 2013 Perseid shower won't affect the Hubble Space Telescope, according to Janet Anderson of NASA's Marshall Space Flight Center in Huntsville, Ala., at other times it might point the opening to its mirrors away from the direction of an outburst of meteors. Other satellites might turn vulnerable antennas away from them as well.

Clouds permitting, Cooke advises skywatchers this year to take their time and enjoy the nighttime show. "All you need is to lie flat on your back, and the reward is meteors."

http://www.usatoday.com/s(...)2013-meteor/2628521/