Orionid Meteor Shower Peak This Weekend
Weekend Meteor Shower
Oct. 20, 2011: Earth is about to pass through a
stream of debris from Halley's comet, source of the annual Orionid
meteor shower. Forecasters expect more than 15 meteors per hour to fly
across the sky on Saturday morning, Oct. 22nd, when the shower peaks.
Orionids are most easily seen during the dark hours before
sunrise. Twilight Orionids, however, are the most beautiful of all.
"Although this isn't the biggest meteor shower of the year, it's
definitely worth waking up for," says Bill Cooke of the NASA Meteoroid
Environment Office. "The setting is dynamite."
Orionids are framed by some of the brightest and most beautiful
constellations in the night sky. The meteors emerge from mighty Orion,
the shower's glittering namesake. From there they streak through Taurus
the Bull, the twins of Gemini, Leo the Lion, and Canis Major--home to
Sirius, the most brilliant star of all.
This year, the Moon and Mars are part of the show. They'll form two vertices of a celestial triangle
in the eastern sky on Saturday morning while the shower is most active;
Regulus is the third vertex. Blue Regulus and red Mars are both
approximately of 1st magnitude, so they are easy to see alongside the
35% crescent Moon. Many Orionids will be diving through the triangle in
the hours before dawn.
Cooke's team at the Meteoroid Environment Office will be watching for Orionids that actually hit the Moon.
Cometary debris streams like Halley's are so wide, the whole
Earth-Moon system fits inside. So when there is a meteor shower on
Earth, there's usually one on the Moon, too. Unlike Earth, however, the
Moon has no atmosphere to intercept meteoroids. Pieces of debris fall
all the way to the surface and explode where they hit. Flashes of light
caused by thermal heating of lunar rocks and moondust are so bright,
they can sometimes be seen through backyard-class telescopes.
A map of the morning sky on Saturday, Oct. 22nd at 5:30 a.m. local time, viewed facing southeast. Click to view a larger, more complete map.
"Since we began our monitoring program in 2005, our group has
detected more than 250 lunar meteors," says Cooke. "Some explode with
energies exceeding hundreds of pounds of TNT."
So far, they've seen 15 Orionids hitting the Moon--"two in 2007,
four in 2008, and nine in 2009," recalls Cooke. This year they hope to
add to the haul. About 25% of the Moon's dark terrain will be exposed
to Halley's debris stream, giving the team millions of square miles to
scan for explosions.
Watching meteoroids hit the Moon is a good way to learn about the
structure of comet debris streams and the energy of the particles
therein. It also allows Cooke and colleagues to calculate risk factors
for astronauts who, someday, will walk on the lunar surface again.
"Going outside to watch the Orionids might not be a good idea for a moonwalker," says Cooke.
But it is a good idea for the res
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