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November
10, 2009: This year's Leonid meteor shower peaks
on Tuesday, Nov. 17th. If forecasters are correct, the shower
should produce a mild but pretty sprinkling of meteors over
North America followed by a more intense outburst over Asia.
The phase of the Moon will be new, setting the stage for what
could be one of the best Leonid showers in years.
 "We're
predicting 20 to 30 meteors per hour over the Americas, and
as many as 200 to 300 per hour over Asia," says Bill
Cooke of NASA's Meteoroid Environment Office. "Our forecast
is in good accord with independent theoretical work by other
astronomers."1
Right:
A Leonid meteor at dawn, photographed in 2002 by Simon Filiatrault
of Quebec, Canada. [larger
image]
Leonids
are bits of debris from Comet Tempel-Tuttle. Every 33 years
the comet visits the inner solar system and leaves a stream
of dusty debris in its wake. Many of these streams have drifted
across the November portion of Earth's orbit. Whenever we
hit one, meteors come flying out of the constellation Leo.
"We
can predict when Earth will cross a debris stream
with pretty good accuracy," says Cooke. "The intensity
of the display is less certain, though, because we don't know
how much debris is in each stream." Caveat observer!
The
first stream crossing on Nov. 17th comes around 0900 UT (4
a.m. EST, 1 a.m. PST). The debris is a diffuse mix of particles
from several old streams that should produce a gentle display
of two to three dozen meteors per hour over North America.
Dark skies are recommended for full effect.
"A
remarkable feature of this year's shower is that Leonids will
appear to be shooting almost directly out of the planet Mars,"
notes Cooke.
It's
just a coincidence. This year, Mars happens to be passing
by the Leonid radiant at the time of the shower. The Red Planet
is almost twice as bright as a first magnitude star, so it
makes an eye-catching companion for the Leonids: sky
map.
The
next stream crossing straddles the hour 2100-2200 UT, shortly
before dawn in Indonesia and China. At that time, Earth will
pass through a pair of streams laid down by Comet Tempel-Tuttle
in 1466 and 1533 AD. The double crossing could yield as many
as 300 Leonids per hour.
Above:
This side of Earth will be facing the Leonid debris stream
at the time of the Nov. 17th outburst. Observers in India,
China and Indonesia are favored with dark, pre-dawn skies.
Image credit: Danielle Moser of the NASA Meteoroid Environment
Office.
"Even
if rates are only half that number, it would still be one
of the best showers of the year," says Cooke.
The
Leonids are famous for storming, most recently in 1999-2002
when deep crossings of Tempel-Tuttle's debris streams produced
outbursts of more than 1000 meteors per hour. The Leonids
of 2009 won't be like that, but it only takes one bright Leonid
streaking past Mars to make the night worthwhile.
Enjoy
the show.
Author: Dr.
Tony Phillips | Credit: Science@NASA
| more
information |
| Footnote:
1Leonid forecasters use computer models to
track the location of debris from Comet Tempel-Tuttle
and to predict Leonid meteor rates when Earth crosses
one of the debris fields. That is the basis for Cooke's
predictions. Here are some others: Jérémie Vaubaillon
of the Institut de Mecanique et de Calcul des Ephemerides
in France predicts 25 meteors per hour over North America
and ~200 per hour over Asia. Another forecaster with
a proven track record, Mikhail Maslov of Russia, predicts
20 to 30 meteors per hour over North American and as
many as 140 per hour over Asia. Earlier
predictions of a "half-storm" of 500+
meteors/hr over Asia have been downgraded.
The
2009 Leonid Meteor Shower -- an overview from the
International Meteor Organization
NASA's
Meteoroid
Environment Office
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