[LM_NET] Meteor Shower Dec. 13-14 in US

[Mary Ludwick <ludwick@SWBELL.NET>]

What could be the best meteor display of the year will reach its peak on the
night of Dec.13-14.
Here is what astronomers David Levy and Stephen Edberg have written of the
annual Geminid Meteor Shower: "If you have not seen a mighty Geminid
fireball arcing gracefully across an expanse of sky, then you have not seen
a meteor."
The Geminids get their name from the constellation of Gemini, the Twins,
because the meteors appear to emanate from a spot in the sky near the bright
star Castor in Gemini.
Also in Gemini this month is the planet Mars, nearing a close approach to
the Earth later this month, and shining brilliantly with yellow-orange hue.
To be sure, Mars is certain to attract the attention of prospective Geminid
watchers this upcoming week.
Reliable shower
The Geminid Meteors are usually the most satisfying of all the annual
showers, even surpassing the famous Perseids of August.
Studies of past find the "Gems" have a reputation for being rich both in
slow, bright, graceful meteors and fireballs as well as faint meteors, with
relatively fewer objects of medium brightness.
They are of medium speed, encountering Earth at 22 miles per second (35
kps). They are bright and white, but unlike the Perseids, they leave few
visible trails or streaks.
They are four times denser than most other meteors, and have been observed
to form jagged or divided paths.
Geminids also stand apart from the other meteor showers in that they seem to
have been spawned not by a comet, but by 3200 Phaethon, an Earth-crossing
asteroid.
Then again, the Geminids may be comet debris after all, for some astronomers
consider Phaethon to really be the dead nucleus of a burned-out comet that
somehow got trapped into an unusually tight orbit.
Interestingly, on Dec. 10, Phaethon will be passing about 11 million miles
(18 million kilometers) from Earth, its closest approach since its discovery
in 1983.
The prospects for this year
The Geminids perform excellently in any year, but British meteor astronomer,
Alastair McBeath, has categorized 2007 as a "great year."
Last year's display was hindered somewhat by the moon, two days past last
quarter phase. But this year, the moon will be at new phase on Dec. 9.
On the peak night, the moon will be a fat crescent, in the south-southwest
at dusk and setting soon after 8 p.m. That means that the sky will be dark
and moonless for the balance of the night, making for perfect viewing
conditions for the shower.
According to McBeath, the Geminids are predicted to reach peak activity on
Dec. 14 at 16:45 GMT.
That means those places from central Asia eastwards across the Pacific Ocean
to Alaska are in the best position to catch the very crest of the shower,
when the rates conceivably could exceed 120 per hour.
"But," he adds, "maximum rates persist at only marginally reduced levels for
some 6 to 10 hours around the biggest ones, so other places (such as North
America) should enjoy some fine Geminid activity as well."
Indeed, under normal conditions on the night of maximum activity, with ideal
dark-sky conditions, at least 60 to 120 Geminid meteors can be expected to
burst across the sky every hour on the average. (Light pollution greatly
cuts the numbers.)
The Earth moves quickly through this meteor stream producing a somewhat
broad, lopsided activity profile.
Rates increase steadily for two or three days before maximum, reaching
roughly above a quarter of its peak strength, then drop off more sharply
afterward.
Late Geminids, however, tend to be especially bright. Renegade forerunners
and late stragglers might be seen for a week or more before and after
maximum.
What to do
Generally speaking, depending on your location, Gemini begins to come up
above the east-northeast horizon right around the time evening twilight is
coming to an end. So you might catch sight of a few early Geminids as soon
as the sky gets dark.
There is a fair chance of perhaps catching sight of some "Earth-grazing"
meteors.
Earth grazers are long, bright shooting stars that streak overhead from a
point near to even just below the horizon. Such meteors are so distinctive
because they follow long paths nearly parallel to our atmosphere.
The Geminids begin to appear noticeably more numerous in the hours after 10
p.m. local time, because the shower's radiant is already fairly high in the
eastern sky by then. The best views, however, come around 2 a.m., when their
radiant point will be passing very nearly overhead.
The higher a shower's radiant, the more meteors it produces all over the
sky.
http://www.space.com/spacewatch/071207-ns-geminids.html
http://www.skyandtelescope.com/observing/highlights/12207486.html
http://science.nasa.gov/headlines/y2007/03dec_asteroidshower.htm


Mary Croix Ludwick
Librarian, Thomas Haley Elementary
Irving, Texas (near Dallas)
mludwick@irvingisd.net
ludwick@swbell.net (home)


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