[meteorite-list] Week-Long Meteor Shower to Dazzle (Geminids)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 8 Dec 2006 11:46:53 -0800 (PST)
Message-ID: <200612081946.LAA11205_at_zagami.jpl.nasa.gov>

http://www.space.com/spacewatch/061208_night_sky.html

Week-Long Meteor Shower to Dazzle
By Joe Rao
SPACE.com
08 December 2006

The annual Geminid meteor shower is expected to produce a reliable
shooting star show that will get going Sunday and peak the middle of
next week.

The Geminid event is known for producing one or two meteors every minute
during the peak for viewers with dark skies willing to brave chilly nights.

If the Geminid Meteor Shower occurred during a warmer month, it would be
as familiar to most people as the famous August Perseids.
Indeed, a night all snuggled-up in a sleeping bag under the stars is an
attractive proposition in summer. But it's hard to imagine anything more
bone chilling than lying on the ground in mid-December for several hours
at night.

But if you are willing to bundle up, late next Wednesday night into
early Thursday morning will be when the Geminids are predicted to be at
their peak.

Most satisfying shower

The Geminids are a very fine winter shower, and usually the most
satisfying of all the annual showers, even surpassing the Perseids.
Studies of past displays show that this shower has 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.
Many appear yellowish in hue. Some even appear to form jagged or divided
paths.

Unfortunately, as was the case this year with its summertime
counterpart, this year's December Geminids will be hindered somewhat by
moonlight, although to a much lesser degree than the brilliant gibbous
Moon that wreaked havoc with the Perseids.

On Thursday morning, the Moon - a fat waning crescent, two days past
last quarter - will come up over the east-southeast horizon by 1:30 a.m.
for most locations and will light up the sky in its general vicinity
through the rest of the overnight hours. On Friday morning, the Moon
will come up about an hour later and will be less of a factor for
meteor watching.

Where to look

These medium speed meteors appear to emanate from near the bright star
Castor, in the constellation of Gemini, the Twins, hence the name
"Geminid."

The track of each one does not necessarily begin near Castor, nor even
in the constellation Gemini, but it always turns out that the path of a
Geminid extended backward passes through a tiny region of sky about
0.2-degree in diameter (an effect of perspective). In apparent size,
that's less than half the width of the Moon. As such, this is a rather
sharply defined radiant as most meteor showers go; suggesting the stream
is "young" - perhaps only several thousand years old.

Generally speaking, depending on your location, Castor begins to come up
above the east-northeast horizon right around the time evening twilight
is coming to an end [sky map
<http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=061208_geminds_02.jpg&cap=Sky+Map%3A+Gemini+at+11%3A30+p.m.+on+Dec.+13+from+mid-northern+latitudes.>].


As Gemini is beginning to climb the eastern sky just after darkness
falls, there is a fair chance of perhaps catching sight of some
"Earth-grazing" meteors. Earthgrazers 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. By around 9 p.m., Gemini will have climbed
more than one-third of the way up from the horizon. Meteor sightings
should begin to increase noticeably thereafter. By around 2 a.m., Gemini
will stand high overhead.

Because Geminid meteoroids are several times denser than the cometary
dust flakes that supply most meteor showers and because of their
relatively slow speed with which they encounter Earth (22 miles/35
kilometers per second), Geminid Meteors appear to linger a bit longer in
view than most. As compared to an Orionid or Leonid meteor that can
whiz across your line of sight in less than a second, a Geminid meteor
moves only about half as fast.

On a personal note, their movement reminds me of field mice scooting
from one part of the sky to another.

When to watch

The Earth moves quickly through this meteor stream producing a somewhat
broad, lopsided activity profile. Hourly rates will start increasing on
Sunday night (Dec. 10), appearing roughly above one-quarter peak strength.

Late Wednesday night up until early Thursday morning when the Moon
rises, a single observer might average as many as 60 to 120 meteors per
hour.

After Wednesday night, the rates are expected to drop off more sharply:
The rates on Thursday night/Friday morning will have diminished to about
30 to 60 per hour. Yet, there is good reason to keep watching for
Geminids even after their peak has passed, for those "late" Geminids,
tend to be especially bright. And renegade late stragglers might be seen
for a week or more after the night of maximum activity.

I brought this up this point earlier, but certainly it should be
addressed again: Make sure you're warm and comfortable. Likely your
local weather will be more appropriate for taking in a hot bath as
opposed to a meteor shower! Warm cocoa or coffee can
take the edge off the chill, as well as provide a slight stimulus.

A final point to note are that Geminids stand apart from the other
meteor showers in that they seem to have been spawned not by a comet,
but by 3200 Phaeton, an Earth-crossing asteroid. Then again, the
Geminids may be comet debris after all, for some astronomers
consider Phaeton to really be the dead nucleus of a burned-out comet
that somehow got trapped into an unusually tight orbit.
Received on Fri 08 Dec 2006 02:46:53 PM PST