(meteorobs) Meteor Activity Outlook for December 23-29, 2005

[Robert Lunsford]

The moon reaches its last quarter phase on Friday December 23rd. At this
time the moon will rise near midnight and will remain in the sky the
remainder of the night. As this period progresses the waning crescent moon
will become less of a nuisance with each passing day. The estimated total
hourly rates for evening observers this week should be near four for
Northern Hemisphere observers and three for those located in the Southern
Hemisphere. For morning observers the estimated total hourly rates should be
near twelve for Northern Hemisphere observers and eight 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.
Morning rates are reduced this week due to moonlight.

The radiant positions listed below are exact for Saturday night/Sunday
morning December 24/25. 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 07:12 (108) +21. This area of the
sky is located in central Gemini, two degrees west of the third magnitude
star Delta Geminorum. Since this radiant is large and diffuse, any slow to
medium speed meteor from Gemini could be a candidate for this shower. 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. Rates should be near three
per hour from the Northern Hemisphere and two per hour for observers south
of the equator. With an entry velocity of 30 km/sec., the average anthelion
meteor would be of medium-slow speed.

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.

The Coma Berenicids (COM) reached maximum activity on December 19, when the
ZHR reaches five. The radiant is currently located at 12:04 (181) +22, which
places it in western Coma Berenicids, eight degrees northeast of the second
magnitude star Denebola (Beta 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 Ursids (URS) reached maximum activity on December 22. Rates are now
falling and will fall below a ZHR of one on December 27. The radiant is
located at 14:28 (217) +75. This area of the sky lies in southern Ursa
Minor, very close to the fourth magnitude star 5 Ursae Minoris. The bright
orange second magnitude star Kochab (Beta Ursae Minoris) also lies only two
degrees to the southeast. This radiant is best placed for viewing just
before dawn, when it lies highest above the horizon. For areas north of
latitude 20 north, the radiant lies above the horizon the entire night. Only
in higher northern latitudes is the radiant altitude sufficient for
unimpeded observing during the evening hours. At 33 km/sec. the Ursids
produce meteors of average velocities.

The Sporadic rates for the Northern Hemisphere are now at their high plateau
for the year. Observers can expect around eight random meteors per hour
during the morning hours as seen from locations in the Northern hemisphere.
During the dark evening hours perhaps four random meteors can be seen per
hour north of the equator. Sporadic rates seen from the Southern Hemisphere
are slowly rising from an October minimum. From south of the equator one
would expect to see approximately six random meteors per hour during the
morning hours and three per hour during the evening.  Morning rates are
reduced due to moonlight.

Anthelion     07:12 (108) +21
Hourly Rate = N. Hemisphere 2 - S. Hemisphere 1

Coma Berenicids (COM)  12:04 (181) +22
Hourly Rate = N. Hemisphere 2 - S. Hemisphere 1

Ursids (URS)  14:28 (217) +75
Hourly Rate = N. Hemisphere <1 - S. Hemisphere 0

Clear Skies!
Robert Lunsford
American Meteor Society