The meteors
that are about to rain down in the early morning of September 1 date from
around 4 A.D., the latest calculations show.
It is not
often that we can tell when a shooting star was first released from a comet
into space, to travel as a meteoroid in an orbit around the Sun, and finally
collide with Earth's atmosphere to shine as a meteor for our enjoyment.
Most meteors that sporadically flash across the sky on a dark moonless night
date from anonymous times. Only in recent years have we learned to trace young
meteor showers, just a few revolutions old, to their date of origin.
The oldest
such shower, but only one revolution old, is due in the early morning of
September 1, 2007. Our calculations indicate Earth is about to cross the dust
trail of comet Kiess, a comet that takes some 2000 years to complete one orbit
around the Sun. The trail is very narrow, so Earth will be hosed by meteoroids
for only about an hour and a half. The meteoroids will approach from the
direction of the constellation Auriga, the charioteer, in the north-eastern
part of the sky, causing a meteor shower called the "Aurigids."
If you spot
one of those meteors, you may be only the fourth person alive who is known to
have seen this meteor shower. In recent times, the shower was spotted in 1994
by two observers and in 1986 by one observer.
If you are
lucky enough to catch a picture of an Aurigid meteor using your digital camera,
you will be the very first to do so.
Tips on how
to observe meteors and where to report the results can be found at: http://aurigid.seti.org
The shower
is visible from only part of the world. If you live in the western parts of the
USA, Canada and Mexico, including Hawaii and Alaska, you might spot an Aurigid
meteor. Plan to step out around 4 A.M. PDT in the early morning, warmly dressed
with a blanket wrapped around your shoulders, away from city smog, with the
Moon behind an obstruction, and with a wide view on the sky. Gaze up at the
sky, waiting, and you may spot one of these elusive bits of matter that Comet
Kiess lost 2000 years ago.
This is
your only chance to see this shower; the dust trail is not going to hit again
in our lifetime. It is also our best chance yet to test meteor shower
prediction models and look for evidence of the crust that a comet is suspected
to build up during the time it spends in the Oort
cloud. Comets in shorter orbits have long lost this pristine crust.
Jon
Giorgini of JPL/Caltech has identified observations of Comet Kiess
when it returned in 1911. The orbit is now better determined than before and
calculating backwards in time puts the comet near Earth's orbit in 4 A.D., give
or take 40 years. It was at that time that the dust was released that we now
see as meteors. The dust was ejected in wider orbits than the comet and took
somewhat longer to return.
Jeremie
Vaubaillon of Caltech calculated where the dust would end up at Earth's orbit
on September 1, 2007, if it was ejected in 4 A.D. and he found that, indeed,
the dust trail will be in Earth's path. The peak is expected at 11:33 UT, or
4:33 a.m. PDT, give or take 20 minutes.
From past
Aurigid showers, we anticipate a shower of mostly -2 to +3 magnitude meteors
with a peak Zenith Hourly Rate about 200 per hour during a 10-minute interval,
with rates above 100 per hour for only 25 minutes. With a bright Moon in the
sky, only 4 days past full, that translates to several tens of chances to make
a wish on a meteor from around 4 A.D.
To increase
our chances of catching these rare meteors, we will be observing the shower
from two Gulfstream GV aircraft (flying at 45,000 ft) on a parallel flight path
from Wisconsin, over the Bay Area in California, and on to the Pacific in the
early morning of September 1. An international team of 24 researchers will have
21 windows to aim their cameras through. The cameras are of different types,
some similar to your own digital camera and camcorder, others using
technologies more familiar to cameras used on astronomical telescopes or those
in night vision goggles. Near the horizon, we hope to see many more meteors
than will be visible from the ground, but each of us will be glad if the shower
actually shows.
You can
participate in this research by making an effort to photograph or film the
Aurigid meteors. Chances are that one of you, not us, will catch the brightest
Aurigid out there. Even simple cameras can provide information about how the
meteoroids break apart, as each image is composed of three different images:
one in blue light, another in green, and one in red. Each color traces
different aspects of the meteor's light.
More
information at our Aurigid Multi-Instrument Aircraft Campaign mission website: http://aurigid.seti.org
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