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Anticipating the Perseids

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Anticipating the Perseids

The 2001 Perseid meteor shower peaks on August 12th. Will it be an extraordinary sky show like last year -- or a moonlit disappointment? Wake up early and find out.

NASA
Marshall Space Flight Center

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see captionJuly 31, 2001: Summer nights and shooting stars. They're an unbeatable combination. That's why northern sky watchers look forward so to the annual Perseid meteor shower in August. During the shower's peak, which happens this year on August 12th, dozens and sometimes hundreds of meteors shoot across the sky every hour. Dark-sky observers who stay out all night sometimes count more than a thousand!

The much-anticipated Perseids, as reliable as clockwork, rarely fail to please. Around this time last year, however, enthusiasts were bracing for something unusual: Perseid disappointment. On the night of the shower's 2000 maximum, the Moon was to be nearly Full. It would outshine all but the brightest shooting stars.

Right: Jimmy Westlake captured this photo of a Perseid meteor streaking through Northern Lights on Aug. 12, 2000. In the foreground is Hahn's Peak, an extinct volcano in Colorado. [more]

Undaunted, sky watchers went outdoors in great numbers. Perhaps it was simply habit. After all, the Perseids have been putting on their annual show for more than two thousand years. Veteran meteor watchers call the shower "Old Faithful" and many figured it might be worth watching in spite of the Moon's glare.

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They were right. Indeed, it was a night that no sky watcher was likely to forget -- ever!

Just as hopeful observers were settling in for a long spell of meteor watching, the sky erupted in color. A billion-ton cloud of electrified gas from the Sun (a "coronal mass ejection") had crashed into Earth's magnetic field and ignited widespread auroras. All across North America sheets of red and green and purple light danced across the sky, stunning onlookers.

That's when the Perseids showed up.

"I couldn't believe my eyes," said an observer from Bishop, CA. Bright Perseid meteors, plentiful after all, were streaking through seldom-seen Northern Lights. "The moonlight hardly mattered," he added.

It just goes to show, you never know what might happen during a night under the stars!

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Above: Douglas Schmutz captured this image of a faint Perseid meteor (visible in the lower middle of an enlarged image) and pink aurora borealis over Hamblin Valley, Utah. [more]

This year experts are again predicting a meager display of Perseids, and the reason sounds familiar. A swollen quarter Moon, bright and shining, will rise at midnight on Sunday, August 12th. By dawn -- just when the shower should be at its best -- the Moon will lie high in the sky. Bright moonlight will likely reduce apparent meteor rates to no more than 20 or 30 per hour.

"That's still a wonderful meteor shower and I recommend trying to see it," says astronomy professor George Lebo, a Summer Faculty Fellow at the NASA Marshall Space Flight Center. "No matter where you live, the best time to watch will be between local midnight and dawn on Sunday morning, August 12th." (Local midnight means midnight in your time zone.) "The Perseids are primarily a northern hemisphere shower," he added. Sky watchers south of the equator won't see nearly as many shooting stars as their northern cousins.

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Above: The sky as seen by an observer at mid-Northern latitudes looking east at 4:00 am local time on August 12, 2001. The red dot denotes the Perseid radiant. Even if you don't see many meteors, the dazzling trio of planets -- Jupiter, Venus, and Saturn -- will make the trip outside worthwhile.

Watching for Perseids is easy. Simply find a dark observing site, away from city lights if possible, and look up toward an unobstructed part of the sky. Meteors will streak overhead. If you trace their tails backwards, most will lead to the constellation Perseus, which contains a point in the sky called "the Perseid radiant."

The Perseid radiant lies near the northeastern horizon at midnight, but it will climb higher as the night wears on. By dawn it will lie about 70 degrees above the northeastern horizon. The Moon -- bright and beautiful, but a real nuisance -- will be in the neighboring constellation Taurus. Like an unwanted guest, the Moon will follow Perseus as it ascends the night sky.

see caption"Don't look in the direction of the Moon," advises Lebo. Instead, face somewhat away from the Perseid radiant with the Moon at your back. Perseid meteors travel far across the sky, so you won't need to look directly toward Perseus to see them. An old meteor watcher's trick is to view a moonlit shower from the shadow of a tall building. The building will block some of the sky, but it will also reduce the Moon's glare.

Above: A colorful Perseid meteor. Credit & Copyright: S. Kohle & B. Koch

Typical Perseid meteors are about as bright as the stars in the Big Dipper -- and many are considerably brighter. If you stay out all night on August 12th, don't be surprised to see several colorful fireballs rivaling the brilliant planet Venus. Such meteors can be seen even from urban areas with light pollution.

Every Perseid meteor that you spot this month is a tiny piece of periodic comet Swift-Tuttle. The comet swings by the Sun at 135 year intervals and leaves behind a trail of dusty debris. Its dust particles strike Earth's atmosphere traveling 59 km/s (132,000 mph). Their extreme speed is the reason that tiny comet particles, most no larger than grains of sand, can produce such dazzling streaks of light. Typical dust specks burn up entirely about 100 km above our planet's surface.

see captionLeft: Tiny comet flakes like this are at the heart of fiery-looking Perseid meteors. This one is only 10 microns across. [more information]

Earth entered the outskirts of Swift-Tuttle's debris stream in late July, and already sky watchers are spotting 3 to 5 Perseids per hour in the predawn sky. Meteor rates will gently climb in the days ahead as Earth approaches the heart of the debris stream. Sometime on August 12th we'll encounter a concentrated filament of comet dust and meteor rates will soar. The shower that everyone has been waiting for will finally be underway.

But will it be worth the wait? Will the 2001 Perseids rival last year's extraordinary show? Or will the Perseids, out of character, disappoint? The best way to find out is to be outdoors that Sunday morning and see for yourself!

Editor's note: On July 23, 2001, a spectacular fireball streaked over the US east coast. It was not an early-arriving Perseid meteor, but rather a small solitary asteroid that probably had nothing to do with comet Swift-Tuttle.

The Perseid
Meteor Shower
July 31, 2001
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Web Links

The Extraordinary Geomagnetic Perseid Meteor Shower -- (Science@NASA) A geomagnetic sto triggered dazzling auroras during the peak of the 2000 Perseid meteor shower.

North American Meteor Network Notes -- August 2001, includes information about the Perseid meteor shower and the mythology of the constellation Perseus.

see captionRight: Herman Mikuz (Crni Vrh Observatory, Slovenia) captured this image of comet 109P/Swift-Tuttle in 1992 during its most recent visit to the inner solar system. Bits of dust shed by Swift-Tuttle are the source of the Perseid meteors. [more]

Perseus -- find out more about this constellation from the Peoria Astronomical Society.

History of the Perseids -- trace the history of the Perseid meteor shower from 36 AD to the present day, from Gary Kronk's Comet & Meteors web site.

Frequently Asked Questions about Fireballs - If you spy a Perseid fireball and want to learn more about such bright meteors, check out this site from the American Meteor Society.


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