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

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 8 Dec 2006 14:53:12 -0600
Message-ID: <003f01c71b0a$e0421ac0$a925e146_at_ATARIENGINE>

Hi,

    Nice timing, since we've been talking about
chunks of comet:

> 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.

    Discovered in 1983, Phaethon is 5100 meters
in diameter and weighs in at 140,000,000 metric
tons. It has a very dark surface and a density
(vaguely) calculated at twice that of water.
    Despite being in a cometary orbit and being
the parent body of a meteor stream in the same
orbit, it has never shown any coma, dust, or
gas outbursts. Dead comet? Asteroid? Or can
we be sure there's really any difference? Yet?
    Phaethon approaches the Sun closer than
any other numbered asteroid; its perihelion is
only 0.140 AU, 58% of Mercury's orbital radius.
The surface temperature at perihelion could
reach ~1025 K.
    Obviously, it's not a ball of "ice."
    If you plan on hanging around until 2093,
it will closely approach the Earth, passing
within 0.0198 AU, on December 14 of that
year. Only a week and 87 years to go.
    3200 Phaethon is one of the objects that fit
unto a pattern of a past breakup of a Comet
Encke parent body, based on its orbital properties,
an admittedly controversial idea (but a good one).
    The asteroid 3200 Phaethon was discovered
as an asteroid, confirmed, plotted, and published,
before Fred ("Mr. Comet") Whipple pointed out
that its orbit was identical with that of the
Geminids.


Sterling K. Webb
---------------------------------------------------------------------------
----- Original Message -----
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Friday, December 08, 2006 1:46 PM
Subject: [meteorite-list] Week-Long Meteor Shower to Dazzle (Geminids)


>
> 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.
>
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Received on Fri 08 Dec 2006 03:53:12 PM PST