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July
22, 2008: Mark
your calendar: The 2008 Perseid meteor shower peaks on August
12th and it should be a good show.
"The
time to look is during the dark hours before dawn on Tuesday,
August 12th," says Bill Cooke of NASA's Meteoroid Environment
Office at the Marshall Space Flight Center. "There should
be plenty of meteors--perhaps one or two every minute."
Right:
A Perseid meteor over Joshua Tree National Park in California,
August 11, 2007. Credit: Joe Westerberg. [more]
The
source of the shower is Comet Swift-Tuttle. Although the comet
is far away, currently located beyond the orbit of Uranus,
a trail of debris from the comet stretches all the way back
to Earth. Crossing the trail in August, Earth will be pelted
by specks of comet dust hitting the atmosphere at 132,000
mph. At that speed, even a flimsy speck of dust makes a vivid
streak of light when it disintegrates--a meteor! Because,
Swift-Tuttle's meteors streak out of the constellation Perseus,
they are called "Perseids."
(Note:
In the narrative that follows, all times are local. For instance,
9:00 pm means 9:00 pm in your time zone, where you live. )
Serious
meteor hunters will begin their watch early, on Monday evening,
August 11th, around 9 pm when Perseus first rises in the northeast.
This is the time to look for Perseid Earthgrazers--meteors that
approach from the horizon and skim the atmosphere overhead like
a stone skipping across the surface of a pond.
"Earthgrazers
are long, slow and colorful; they are among the most beautiful
of meteors," says Cooke. He cautions that an hour of
watching may net only a few of these at most, but seeing even
one can make the whole night worthwhile.
A
warm summer night. Bright meteors skipping overhead. And the
peak is yet to come. What could be better?
The
answer lies halfway up the southern sky: Jupiter and the gibbous
Moon converge on August 11th and 12th for a close encounter
in the constellation Sagittarius: sky
map. It's a grand sight visible even from light-polluted
cities.
For
a while the beautiful Moon will interfere with the Perseids,
lunar glare wiping out all but the brightest meteors. Yin-yang.
The situation reverses itself at 2 am on Tuesday morning,
August 12th, when the Moon sets and leaves behind a dark sky
for the Perseids. The shower will surge into the darkness,
peppering the sky with dozens and perhaps hundreds of meteors
until dawn.
Above:
The eastern sky viewed during the hours before sunrise on
Tuesday, Aug. 12, 2008.
For
maximum effect, "get away from city lights," Cooke
advises. The brightest Perseids can be seen from
cities, he allows, but the greater flurry of faint, delicate
meteors is visible only from the countryside. (Scouts,
this is a good time to go camping.)
The
Perseids are coming. Enjoy the show!
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Author: Dr.
Tony Phillips | Credit: Science@NASA
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