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(meteorobs) Meteor Activity Outlook for December 14-20, 2001
The moon is new on Friday December 14 and will emerge into the evening
sky early next week. This will allow excellent viewing of the Geminid
meteor shower which peaks on Thursday night/Friday morning December
13/14. The estimated total hourly rates for evening observers this week
should be near 5 for those in the Northern Hemisphere and 1 for those in
the Southern Hemisphere. For morning observers the estimated total
hourly rates should be near 30 for the Northern Hemisphere and 15 for
those located in the Southern Hemisphere. These rates assume that you
are watching from rural areas away from all sources of light pollution.
The actual rates will also depend on factors such as personal light and
motion perception, local weather conditions, alertness and experience in
watching meteor activity.
The positions listed below are exact for Saturday night/Sunday morning
December 15/16. The positions do not change greatly day to day so they
may be used during this entire period. Most star atlas's (available at
science stores and libraries) will provide maps with grid lines of the
celestial coordinates so that you may find out exactly where these
positions are located in the sky. A planisphere or computer planetarium
program is also useful in showing the sky at any time of night on any
date of the year. Activity from each radiant is best seen when it is
positioned highest in the sky, either due north or south along the
meridian, depending on your location. Meteor activity is not seen from
radiants that are located below the horizon. The radiants are listed in
a west to east manner in order of right ascension (celestial longitude).
The radiants listed first are located further west therefore are
accessible earlier in the night while those listed last rise later in
the night. This list also provides the order of ascending velocity for
each radiant with those listed first being much slower than those last
on the list. Velocity should not be the prime factor for shower
association as all showers can produce slow meteors. Slow meteors would
be seen near the radiant or close to the horizon. The true velocity is
only revealed in shower members seen far from the radiant and high in
the sky.
The Antihelion radiant is now located at 06:36 (099) +23. This area of
the sky is located in western Gemini 4 degrees east of the 3rd magnitude
star Mu Geminorum. Any slow to medium speed meteor from eastern Taurus,
northern Orion or western Gemini may be a good candidate for this
shower. This area of the sky is best placed near 0100 local standard
time when it lies on the meridian and is highest in the sky. At this
time expect to see at least 2 shower members per hour from locations in
the Northern Hemisphere. Observers south of the equator will most likely
see 1 per hour. Unlike most of the annual showers the antihelion radiant
is produced by debris from unknown sources orbiting in a direct motion
like the earth. These sources are most likely asteroids, which produce
stony and metallic debris whose density is much greater that produced by
comets. This debris collides with the earth on the inbound portion of
its orbit, before its closest approach to the sun. Therefore we best see
them just after midnight when we are facing the direction from which
this activity appears. The antihelion radiant is active all year from an
area of the sky nearly opposite that of the sun. The radiant will travel
approximately one degree eastward per day and travels through many
different constellations over the course of a year. It is easiest to
simply list these meteors as "ANT" but a majority of meteor
organizations prefer that you list them from the constellation in which
the radiant is currently located or the constellation where the shower
reaches maximum activity. For instance those who share reports with the
IMO should now label these meteors as "Chi Orionids" (XOR).
The Monocerotids reached maximum activity on December 9. The radiant is
currently located at 7:00 (105) +08 which places it in eastern Monoceros
5 degrees west of Beta Canis Minoris. Current hourly rates are expected
to be near 1. The radiant is best placed for observing near 0100 local
time. These meteors would be of medium velocity.
The Geminids will reach maximum activity Thursday night/Friday morning
December 13/14 from a radiant located at 7:28 (112) +33. This area of
the sky lies in Northern Gemini just north of the bright star Castor
(Alpha Geminorum). For those in the Northern Hemisphere Castor rises
shortly after dusk therefore Geminid activity may be seen all night
long. The Geminids are best seen between 0100 and 0200 when the radiant
lies highest in the sky. Rates could surpass 100 meteors per hour at
maximum if seen from rural sites. By Saturday rates will have fallen
below 50/hr and then less than 20/hr by Sunday. Geminids may be seen
from the Southern Hemisphere at a much reduced rate due to the low
radiant altitude from that vantage point. The Geminids are of medium
velocity. They are noted for their vividly colored fireballs which
should appear in abundance near maximum activity. The Geminids are also
the only major annual shower known to be produced by an asteroid
(1980 TB). This fact has only been known for the last 20 years.
The Sigma Hydrids reached maximum activity on December 11 with a peak
rate of 3 meteors per hour. The current radiant position lies at 08:44
(131) +01 which places it in extreme western Hydra, near the serpent's
head. Shower members would be swift. The best time to view activity from
this radiant would be near 0300 local time.
The Zeta Puppids are listed among the radiants of the Dutch Meteor
Society. This weak shower peaked on November 13th. The current radiant
position is located at 09:20 (140) -52. This area of the sky is located
in central Vela 5 degrees north of the 2nd magnitude star Kappa Velorum.
This radiant is better placed for observers located south of the equator
when it is seen much higher in the sky. These observers may see 1-2
shower members per hour at maximum. The radiant is best placed in the
sky near 0400 when it lies highest in the sky. Any shower members would
be of medium speed if seen far from the radiant and high in the sky. If
seen close to the radiant or low in the sky they would appear to move
more slowly.
The Northern Apex radiant is now located at 11:36 (174) +17. This
position lies in eastern Leo 3 degrees northwest of the 2nd magnitude
star Denebola (Beta Leonis). This area of the sky is best placed for
viewing during the last dark hour before dawn. Since this radiant is
diffuse any meteors from eastern Leo could be a good candidate for this
shower. As seen from the Northern Hemisphere this source should produce
2-3 meteors per hour during the last few hours before dawn. Rates seen
from the Southern Hemisphere would be much less at 0-1 per hour due to
the low radiant altitude seen south of the equator. Those who send
reports to the I.M.O. should label these meteors as Coma Berenicids
(COM).
Like the antihelion radiant both apex radiants are active all year long
and travel approximately one degree eastward per day. Unlike the
antihelion debris these particles orbit the sun in a retrograde motion
opposite that of the earth and are most likely produced by unknown
comets. They strike the earth after their closest approach to the sun.
Since they are moving in opposite directions these particles strike the
earth at tremendous velocities often creating bright meteors with
persistent trains. These particles strike the earth on the morning side
of earth and are best seen just before morning twilight while the sky is
still perfectly dark. There are meteors with a zero inclination that
radiate precisely from the apex point on the ecliptic, exactly 90
degrees west of the sun. These meteors are rare though as the earth
orbits the sun it "sweeps clean" much of the material that shares the
same orbit. Much more debris is located just north and south of the
earth's orbit with slightly higher or lower inclinations. This creates
the northern and southern branches of the apex activity. Meteors from
both branches are normally included in the sporadic count but should
also be noted in some manner as to which branch of the apex complex they
appear to radiate.
The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 11:36 (174) -13. This position lies in the dim
constellation of Crater. Like the northern apex these meteors are best
seen toward dawn when the radiant lies highest above the horizon in a
dark sky. Any meteor from Crater or southeastern Leo could be a
candidate from this source. Rates should be close to 2 per hour from
most locations.
The Ursids reach a ZHR of 1 on December 17. Rates will improve as we
approach the December 22 maximum. The current radiant position is 14:28
(217) +78 which places it in Ursa Minor near the bright star Kochab
(Beta Ursae Minoris). These are medium speed meteors that are best seen
just before dawn when the radiant lies highest in the sky. Due to its
high declination (celestial latitude) these meteors are not visible from
the Southern Hemisphere.
The Sporadic rates for the Northern Hemisphere are now near 8 meteors
per hour during the last hours before dawn from rural observing sites.
This estimate and the morning estimate for the Southern Hemisphere does
not include the apex meteors listed above. During the evening hours
perhaps 3 random meteors can be seen per hour from the Northern
Hemisphere. Rates seen from the Southern Hemisphere are now near their
annual low with perhaps 3 random meteors being seen per hour during the
late morning hours and 1 per hour during the evening.
Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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