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August 7, 2006: Blame it on the Moon: The 2006
Perseid meteor shower is going to be a dud. Oh, Earth will pass
through the Perseid meteoroid stream, as usual. And meteors
will flit across the sky. But when the shower peaks on August
12th and 13th, the glare of the 87%-full Moon will overwhelm
most Perseids, making them impossible to see.
That
sounds like the end of the story—but
don't stop reading.
You might see some Perseids,
after all. The trick is to look before the Moon rises. Plan
your meteor watch for 8:30 p.m. to 10 p.m. on Saturday, August
12. The Moon won't be up yet and, in the darkness just after
sunset, a special kind of meteor may appear: the Perseid Earthgrazer.
(Note:
Because the Perseid peak
is broad, Friday evening, August 11, may be as good or better
than Saturday evening, August 12. If you're ambitious, try both
nights between 8:30 p.m. and 10:00 p.m. local time.)
Earthgrazers
are meteors that skim the top of Earth's atmosphere like a
stone skipping across the surface of a pond. They appear when
the radiant of a meteor shower is near the horizon, spewing
meteoroids not down, but horizontally overhead. Such will
be the case on Saturday evening after sunset when Perseus
(the radiant of the Perseids) first peeks over the northern
horizon.
Don't
expect a storm. Earthgrazers are rare. An hour's watching
might net no more than one or two, but that's plenty. Earthgrazers
are colorful and gracefully slow. People who see one talk
about it for years.
Looking
for Earthgrazers is simple: Spread a blanket on the ground,
lie down and look up. A reclining lawn chair facing north
works just as well. Perseid Earthgrazers streak overhead,
flying generally north to south.
If
you haven't spotted an Earthgrazer by 10 p.m., you probably
won't. By 10 p.m., Perseus will have risen too high in the
sky for grazing meteoroids. (Try skipping a stone by throwing
it down into a pond and you'll see the problem.) Plus, the
Moon itself rises around 10 p.m. to put a real damper on things.
Above:
Sky map, looking north after sunset, Saturday evening, Aug.
12, 2006. [Larger
map]
The
rest of the night is for contrarians, people who stay up until
dawn in spite of the moonlight. They'll see some Perseids,
a small fraction of the norm, to be sure, but not zero. Occasionally,
a really bright fireball might streak across the sky, making
the long night worthwhile. It pays to resist!
Next
year will be better. The 2007 Perseids peak with no Moon in
sight. Until then, watch out for Earthgrazers.
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Note:
All times in this story are local to the reader. So, "plan
your meteor watch for 8:30 to 10 p.m." means go outside
between 8:30 and 10:00 p.m. local time, no matter where you
live. The Perseid meteor shower is best seen from the northern
hemisphere.
Author: Dr. Tony
Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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