(meteorobs) Meteor Activity Outlook for December 10-16, 2004

[Robert Lunsford]

This upcoming period will see the moon reaching its new phase on Sunday
December 12. With the moon totally out of the way for late night/early
morning observing, this will be the best week of the month to view meteor
activity. It is exceptionally fortunate that the Geminid meteor shower
reaches maximum activity during this period. The estimated total hourly
rates (for Sunday December 12) for evening observers this week should be
near ten for those in the Northern Hemisphere and three for those observers
south of the equator. For morning observers the estimated total hourly rates
should be near sixty for those located in the Northern Hemisphere and
twenty for those 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 radiant positions listed below are exact for Saturday night/Sunday
morning December 11/12. These positions do not change greatly day to day so
the listed coordinates may be used during this entire period. Most star
atlases (available at science stores and planetariums) 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 latitude. Meteor activity is not seen from
radiants that are located below the horizon. The positions below are listed
in a west to east manner in order of right ascension (celestial longitude).
The positions listed first are located further west therefore are accessible
earlier in the night while those listed further down the list rise later in
the night.

These are the showers that may be observed this week:

The Anthelion radiant is now centered at 06:20 (095) +23. This area of the
sky is located in western Gemini, very close to the third magnitude star Eta
Geminorum. Since this radiant is large and diffuse, any slow to medium speed
meteor from northern Orion, southeastern Auriga, western Gemini,
northwestern Monoceros or eastern Taurus could be a candidate for this
shower. Be aware that the Geminid and Monocerotid radiants lie just fifteen
degrees to the northeast and southeast. The center of this area 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 three shower members per hour
from the Northern Hemisphere and one per hour south of the equator.

Unlike most of the annual showers the antihelion source is produced by
debris from unknown objects orbiting in a direct motion like the earth.
These objects are most likely asteroids, which produce stony and metallic
debris whose density is much greater than material produced by comets. There
is also the possibility that some of this activity may be caused by the
"Jupiter family of comets", comets which have been altered by Jupiter's
gravity into much shorter orbits. This material 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 source is active
all year from an area of the sky nearly opposite that of the sun. The center
of this source will move approximately one degree eastward per day and
travels through many different constellations over the course of a year. It
may make sense to list these meteors as anthelions or "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. IMO observers should label these meteors as the
Chi Orionids (XOR).

The Monocerotids (MON) are currently active from a radiant located at 06:48
(102) +08. This area of the sky is located in northwestern Monoceros, five
degrees south of the third magnitude star Xi Geminorum. These meteors are
best seen near 0100 local standard time when the radiant lies highest above
the horizon.  The peak for the Monocerotids occurred on December 8 when the
ZHR reached three. This shower would be equally well seen from both
hemispheres. At 42 km/sec. the Monocerotids produce meteors of average
velocity.

The Geminids (GEM) reach maximum activity on December 13 near 22:20
Universal Time. Rates seen twelve hours either side of this time will
witness substantial activity. While it may be advantageous to have the
radiant high above during this time, observers the world over still have an
opportunity on December 13 and 14 to view an impressive shower. The only
locations not able to witness the show will be those in the Southern
Hemisphere south of 30 degrees south latitude, as the radiant will not rise
above the horizon from there. The radiant is located at 07:20 (110) +33.
This area of the sky is located in northern Gemini, five degrees northwest
of the second magnitude Castor (Alpha Geminorum). These meteors are best
seen near 0200 local standard time when the radiant lies highest above the
horizon. This shower is best suited for the Northern Hemisphere but some
activity can be seen south of the equator when the radiant culminates low in
the northern sky. At 35 km/sec. the Geminids produce meteors of average
velocity. More details on viewing the Geminid meteor shower will be posted
on "meteorobs" shortly.

The Puppid-Velids (PUP) is a vast complex of weak radiants similar to the
Virginid showers of March and April. Visual plots and photographic studies
have revealed many radiants in this area during November and December. The
DMS's Zeta Puppid radiant of November is no doubt part of this complex. The
combined strength of these radiants can produce a ZHR of ten. Actual hourly
rates will be much less unless you happen to be observing from the deep
Southern Hemisphere. The center of this activity is currently located at
08:24 (126) -45. This position lies in western Vela, three degrees northeast
of the second magnitude star Gamma Velorum. These meteors are best seen near
0300 local standard time when the radiant lies highest above the horizon in
a dark sky. Observers located in the Southern Hemisphere have an advantage
viewing this shower as the radiant will rise higher into their sky allowing
more activity to be seen. At 41 km/sec. the Zeta Puppids produce meteors of
average velocity.

The Sigma Hydrids (HYD) are currently active from a radiant located at 08:32
(128) +02. This area of the sky is located in western Hydra, only one degree
southwest of the fourth magnitude star Sigma Hydrae. These meteors are best
seen near 0300 local standard time when the radiant lies highest above the
horizon.  The predicted peak for the Sigma Hydrids occurs on December 12
when the ZHR reaches two. At 58 km/sec. the Sigma Hydrids produce meteors of
average to swift velocity.

The Coma Berenicids (COM) reach a ZHR of one on December 12. Maximum
activity is predicted to occur near December 19, when the ZHR reaches five.
The radiant is currently located at  11:24 (171) +27, which places it in
northeastern Leo, six degrees northeast of the third magnitude star Zosma
(Delta Leonis). This radiant is best placed for viewing just before dawn,
when it lies highest above the horizon. At 65 km/sec. the Coma Berenicids
produce mostly swift meteors with the brighter shower members leaving
persistent trains.

The Sporadic rates for the Northern Hemisphere are now near their annual
peak. One would expect to see perhaps twelve random meteors per hour during
the last hours before dawn from rural observing sites. During the evening
hours perhaps three random meteors can be seen per hour from the Northern
Hemisphere. Rates seen from the Southern Hemisphere are now lower than those
seen in the north with perhaps eight random meteors being seen during the
late morning hours and two per hour during the evening.

Anthelion (XOR)   Radiant Position  = 06:20  (095)  +23
Hourly Rate = 3  N. Hemisphere, 1  S. Hemisphere

Monocerotids (MON)   Radiant Position  = 06:48  (102)  +08
Hourly Rate = 1  N. Hemisphere, 1  S. Hemisphere

Geminds (GEM)   Radiant Position  = 07:20  (110)  +33
Hourly Rate = 40  N. Hemisphere,  5  S. Hemisphere

Puppid-Velid (PUP)   Radiant Position  = 08:24  (126)  -45
Hourly Rate = 1  N. Hemisphere, 3  S. Hemisphere

Sigma Hydrid (HYD)   Radiant Position  = 08:32 (128)  +02
Hourly Rate = 1  N. Hemisphere, 1  S. Hemisphere

Coma Berenicid (COM)   Radiant Position  = 11:24 (171)  +27
Hourly Rate = 1  N. Hemisphere, 0  S. Hemisphere


Clear Skies!
Robert Lunsford
American Meteor Society