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October
19, 2009: The Orionid meteor shower peaks this week
and it could be a very good show.
"Earth
is passing through a stream of debris from Halley's Comet,
the source of the Orionids," says Bill Cooke of NASA's
Meteoroid Environment Office. "Flakes of comet dust hitting
the atmosphere should give us dozens of meteors per hour."
 The
best time to look is before sunrise on Wednesday, Oct. 21st.
That's when Earth encounters the densest part of Halley's
debris stream. Observing is easy: Wake up a few hours before
dawn, brew some hot chocolate, go outside and look up. No
telescope is required to see Orionids shooting across the
sky.
Right:
An Orionid meteor photographed on Oct. 21, 2008, by amateur
astronomer Rich Swanson of Sierra Vista, Arizona. [more]
Orionids
appear every year around this time when Earth orbits through
an area of space littered with debris from the ancient comet.
Normally, the shower produces 10 to 20 meteors per hour, a
modest display. The past few years, however, have been much
better than usual.
"Since
2006, the Orionids have been one of the best showers of the
year, with counts of 60 or more meteors per hour," says
Cooke.
According
to Japanese meteor scientists Mikiya Sato and Jun-ichi Watanabe,
2006 marked Earth's first encounter with some very old debris.
"We have found that the [elevated activity of 2006] was
caused by dust trails ejected from 1P/Halley in 1266 BC, 1198
BC, and 911 BC," they wrote in the August 2007 edition
of Publications of the Astronomical Society of Japan.
In their paper "Origin of the 2006 Orionid Outburst,"
Sato and Watanabe used a computer to model the structure and
evolution of Halley's many debris streams stretching back
in time as far as 3400 years. The debris that hit Earth in
2006 was among the oldest they studied and was rich in large
fireball-producing meteoroids.
Repeat
encounters produced good displays in 2007 and 2008—and "the
meteoroids are expected to approach Earth [again] in 2009,"
say Sato and Watanabe. They note that these old broad streams
tend to produce equally broad showers, lasting several nights
around the peak. So, if clouds interfere on the 21st, try
again on the 22nd or 23rd.
Above:
Orionid meteors stream from the elbow of Orion the Hunter.
Because the shower's radiant point is close to the celestial
equator, sky watchers in both hemispheres can enjoy the show.
[larger map]
The
phase of the Moon favors a good show. The Moon is almost new
and completely absent from the pre-dawn sky at the time of
the shower's peak. Bright moonlight will not be a problem.
Last
but not least, the display will be framed by some of the prettiest
stars and planets in the night sky. In addition to Orionids,
you'll see brilliant Venus, red Mars, the dog star Sirius,
and bright winter constellations such as Orion, Gemini and
Taurus. Even if the shower is a dud, the rest of the sky is
dynamite.
Set
your alarm and enjoy the show.
Author: Dr.
Tony Phillips | Credit: Science@NASA
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