http://news.nationalgeographic.com/news/2008/08/080807-perseids.html
Graeme Stemp-Morlock
for National Geographic News
August 7, 2008
Unlike short-lived solar eclipses or unpredictable auroras, meteor showers regularly offer
skywatchers a dazzling show.
Soon the curtain will rise on one of the best of these showers: the Perseids, so called because the
meteors appear to originate in the constellation Perseus.
Slated to peak sometime during the night and early morning of August 11 to 12, the shower offers one
of the year's best chances to see a shooting star.
Under perfect conditions, observers can expect to see about 90 to100 meteors an hour, said Wayne
Hally, a self-professed "meteor geek" who writes a newsletter for the North American Meteor Network.
Hally spends a few hundred hours a year watching for meteors from his base in northwest New Jersey.
The stargazer said he expects the Perseids to have a sustained peak over several hours this year.
"Based on last year's results, it appears that the actual peak was not at a specific time but lasted
a day and a half surrounding that date," Hally said.
"The peak [this year] might be the whole night."
A Blaze of Glory
Meteor showers happen regularly when Earth plows through a stream of dust and small rocks trailed by
a comet after its close approach to the sun.
109P Swift-Tuttle, the comet responsible for the Perseid meteor shower, orbits the sun every 133
years. The comet last made a close approach in 1992, resulting in a spectacular meteor shower with
rates four times higher than average.
"The Perseids have been seen since 36 A.D., almost 2,000 years ago. Most [meteor showers] have not
been around that long, as streams spread out," Hally said.
"The comet that produces the Perseids is in a good reliable orbit. So it's been around for 2,000
years, and it will probably be around for another 2,000."
"Free Sample"
More than just a pretty spectacle, meteors offer astronomers a glimpse back in time to when planets
formed.
Paul Wiegert, a physicist and astronomer at Canada's University of Western Ontario, studies meteors
with the Meteor Physics Group, the largest research body of its kind in North America.
"[Comets] are interesting because they are extremely old, forming when planets did, and they are
unaltered since. With comets, you can observe what went into making the Earth, its original
ingredients," Wiegert said.
Occasionally pieces of comet debris survive the fiery descent through our atmosphere and crash into
Earth as meteorites.
"Meteorites can be billions of years old, much older than anything on Earth," Wiegert said.
"It's like a free sample of material from outer space. Space missions cost millions of dollars to go
get that material, but sometimes we can get it delivered here for free."
Starry Nights
Observers on the U.S. West Coast will likely get the best view of the peak just before dawn on
August 12.
But the Perseids will put on a good show as seen from almost any place on Earth for several reasons.
The moon will set relatively early, making the sky darker and allowing observers to see fainter
meteors.
Also, the region in the sky where the meteors appear to come from will rise up higher as the night
progresses, so fewer meteors will shoot below the horizon.
Meteors higher in the sky also appear brighter, because they are seen through less
distortion-causing atmosphere.
Hally, the meteor buff, says that people who want to see the largest number of meteors possible
should find the darkest sky available and face northeast, where the meteors will appear to come
from.
And don't forget a warm blanket. Even August can feel cold with the early morning dew, he noted. A
reclining deck chair can also help reduce neck strain from looking up.
"[W]ith meteors, you never know exactly what you are going to get," Hally said. "With a telescope on
a star cluster, it will look the same today as the next hundred years.
"If you look at the planets, you don't see a lot of change. But with a meteor shower you never
really know what's going to happen."
Jan Rasmussen