(meteorobs) Meteor Activity Outlook for December 9-15, 2005

Robert Lunsford lunro.imo.usa at cox.net
Fri Dec 9 11:08:03 EST 2005


The moon reaches its full phase on Thursday December 15th. At this time the
moon will rise as the sun sets and set as the sun rises. This weekend will
offer a window of opportunity as the waxing gibbous moon will set a few
hours before the start of morning twilight. This window gets smaller as the
week progresses as the moon sets later in the morning with each passing day.
The estimated total hourly rates for evening observers this week should be
near three for Northern Hemisphere observers and two for those located in
the Southern Hemisphere. For morning observers the estimated total hourly
rates should be near twenty for Northern Hemisphere observers and fifteen
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.  Evening rates are reduced this week due to moonlight.

The radiant positions listed below are exact for Saturday night/Sunday
morning December 10/11. 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 06:16 (094) +23. This area of the
sky is located in western Gemini, one degree north of the third magnitude
star Eta Geminorum. Since this radiant is large and diffuse, any slow to
medium speed meteor from northern Orion, western Gemini, southern Auriga, or
eastern Taurus 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 two per hour from the
Northern Hemisphere and one 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. Those who send their reports to the International
Meteor Organization (IMO) should list these meteors as Chi Orionids (XOR)
depending on whether the meteors radiate from south or north of the
ecliptic.

The Monocerotids (MON) are currently active from a radiant located at 06:44
(101) +08. This area of the sky is located in northern Monoceros, halfway
between the bright stars Betelgeuse (Alpha Orionis) and Procyon (Alpha Canis
Minoris). 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 reaches 3. This shower would be equally
well seen from both hemispheres. At 42 km/sec. the Monocerotids produce
meteors of average velocity. Don't confuse this shower with the short
duration Alpha Monocerotids, which were active last month.

The Geminids (GEM) reach maximum activity on December 14 near 3:30 Universal
Time. For those in North American this occurs during the early evening hours
of December 13. With the moon nearly full this display will be substantially
reduced. Those with clear, transparent skies may be able to see up to thirty
Geminids per hour at best. The best time to view, regardless of your
location will be between the hours of 0100 and 0200 on the morning of
December 14, when the Geminid radiant lies highest in the sky. Be sure to
keep the bright moon at your back while viewing. The radiant is currently
located at 07:16 (109) +33. This area of the sky is located in northern
Gemini, five degrees northwest of the second magnitude Castor (Alpha
Geminorum). 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. The Geminids are known for producing bright and colorful
fireballs.

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
08:20 (125) -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 08:24
(126) +02. This area of the sky is located in western Hydra, three degrees
west 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. Recent studies have indicated that this shower may peak
earlier in the month so careful monitoring early during this period would be
valuable. 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 11:20 (170) +27, which places it in
northeastern Leo, five 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 at their high plateau
for the year. Observers can expect around twelve random meteors per hour
during the morning hours as seen from locations in the Northern hemisphere.
During the dark evening hours perhaps three 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 eight random meteors per hour during the
morning hours and two per hour during the evening.  Evening rates are
reduced due to moonlight.

Anthelion     06:16 (094) +23
Hourly Rate = N. Hemisphere 3 - S. Hemisphere 2

Monocerotids (MON)   06:44 (101) +08
Hourly Rate = N. Hemisphere 1 - S. Hemisphere 1

Geminids (GEM)   07:16 (109) +33
Hourly Rate = N. Hemisphere 5 - S. Hemisphere 1

Puppid-Velids (PUP) 08:20 (125) -45
Hourly Rate = N. Hemisphere <1 - S. Hemisphere 2

Sigma Hydrids (HYD)  08:24 (126) +02
Hourly Rate = N. Hemisphere 1 - S. Hemisphere 1

Coma Berenicids (COM)  11:20 (170) +27
Hourly Rate = N. Hemisphere <1 - S. Hemisphere <1

Clear Skies!
Robert Lunsford
American Meteor Society



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