(meteorobs) Meteor Activity Outlook for December 14-20, 2007

[Robert Lunsford]

No matter where you live, the first half of December provides some of the
best meteor activity of the year. In the northern hemisphere the sporadic
rates are still strong plus you can also count on strong activity from the
Geminids, which peak on December 14. There are also several minor radiants
that add a few meteors each hour. All of these centers of activity are
located high in the sky during the early morning hours this time of year.
The night of December 13/14 is no doubt the best night of the year to view
meteor activity. The moon is favorable during this entire period. After the
15th, the shower activity suddenly wanes and a great majority of the
activity seen is sporadic. Approaching Christmas the moon become a major
factor and ruins the maximum of the Ursid shower.

As seen from the southern hemisphere the sporadic rates are increasing
toward a January maximum. Shower rates are also good but the Geminids suffer
a bit from the lower elevation seen from southern locations. Still with the
warmer weather now occurring south of the equator, December is a great time
to view celestial fireworks.

During this period the moon reaches its first quarter phase on Monday
December 17. At this time the moon will be located ninety degrees east of
the sun and will set near midnight local standard time (LST). This weekend
the moon will not be a factor as it sets before the best meteor activity
occurs during the morning hours. Toward the end of this period the waxing
gibbous moon will only allow a couple of hours of dark skies between moonset
and the start of morning twilight. The estimated total hourly rates for
evening observers this week is near three for those located in the
mid-northern hemisphere (45 N) and one for observers from the mid-southern
hemisphere (45 S). For morning observers the estimated total hourly rates
should be near twenty-five for those located in the mid-northern hemisphere
(45 N) and fifteen for those viewing from the mid-southern hemisphere (45
S). 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 by moonlight.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning December 15/16. 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. It must be remembered that
meteor activity is rarely seen at the radiant position. Rather they shoot
outwards from the radiant so it is best to center your field of view so that
the radiant lies at the edge and not the center. Viewing there will allow
you to easily trace the path of each meteor back to the radiant (if it is a
shower member) or in another direction if it is a sporadic. 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.

The following showers are expected to be active this week:

The Earth has now passed the stream of particles produced by comet 2P/Encke,
which gives us the Taurid meteors each autumn. As we enter the month of
December we again recognize the ever present Antihelion (ANT) radiant. This
large, diffuse radiant is now centered at 06:28 (097) +23. This position
lies in western Gemini near the third magnitude star Mu Geminorum. This area
of the sky is best placed on the meridian near 0100 local standard time
(LST). One can expect to see approximately three shower members per hour as
seen from the northern hemisphere and two per hour from south of the
equator. At 30km/sec., the average Antihelion meteor travels slowly through
the skies.

The Monocerotids (MON) are currently active from a radiant located at 07:00
(105) +08. This area of the sky is located in northeastern Monoceros, ten
degrees northwest of the zero magnitude star Procyon (Alpha Canis Minoris).
These meteors are best seen near 0100 LST when the radiant lies highest
above the horizon. The peak for the Monocerotids was December 8 and weak
activity continues until December 16. This shower would be equally well seen
from both hemispheres. Current rates are most likely near one per hour. At
42 km/sec. the Monocerotids produce meteors of average velocity.

The Geminids (GEM) peak(ed) on the night of December 13/14. Rates will
quickly fall this weekend and the show will basically be over by the 17th.
Current rates would be near five shower members per hour as seen from the
mid-northern latitudes and only one per hour from the mid-southern
latitudes. The current radiant is located at 07:36 (114) +33. This area of
the sky is located in northern Gemini, just north of the second magnitude
star Castor (Alpha Geminorum). These meteors are best seen near 0200 LST
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.

The Sigma Hydrids (HYD) may be weakly seen from a radiant located at 08:44
(131) +01. This area of the sky is located in western Hydra, only one degree
south of the five faint stars that make up the "head" of Hydra. 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 occurred
on December 12 when the ZHR reaches two. Current rates are expected to be
less than one shower member per hour. At 58 km/sec. the Sigma Hydrids
produce meteors of average to swift velocity.

The Coma Berenicids (COM) are active from a radiant located at 11:32 (173)
+26. This area of the sky is located in northwestern Coma Berenices, six
degrees northeast of the third magnitude star Zosma (Delta Leonis). This
radiant is probably responsible for the many reports of activity in Leo
during the month of December. Current rates would be near one shower member
per hour. These meteors are best seen near 0600 local standard time when the
radiant lies highest above the horizon. At 65 km/sec. the Coma Berenicids
will usually produce meteors of swift velocity.

Sirko Molau's study of video radiants has revealed activity during the
period December 19-24, from an area in northern Virgo. Maximum occurs on
December 20 with the radiant located at 13:28 (202) +09. This position lies
five degrees southeast of the third magnitude star Vindemiatrix (Epsilon
Virginis). This radiant is best placed during the last dark hour before dawn
when it lies highest in a dark sky. Rates are most likely less than one
shower member per hour. no matter your observing location. At 62km/sec., the
average meteor from this radiant would be swift.

Sporadic rates have reached maximum for observers in the northern hemisphere
and are now slowly rising for those located south of the equator. One would
expect to see approximately fifteen random meteors during the last hour
before dawn from rural observing sites in the mid-northern hemisphere (45
N). During the first dark hour after the end of evening twilight, perhaps
three random meteors can be seen per hour. As seen from the mid-southern
hemisphere (45 S) late morning rates would now be near eleven per hour.
During the first dark hour after the end of evening twilight, perhaps one
random meteors can be seen per hour. Evening rates are reduced due to
moonlight.

Antihelion (ANT) - 06:28 (097) +23
Northern Hemisphere - 3   Southern Hemisphere - 2

Monocerotids (MON)  07:00 (105) +08
Northern Hemisphere - 1   Southern Hemisphere - 1

Geminids (GEM)  07:36 (114) +33
Northern Hemisphere - 5   Southern Hemisphere - 1

Sigma Hydrids (HYD)  08:44 (131) +01
Northern Hemisphere - <1   Southern Hemisphere -<1

Coma Berenicids (COM)  11:32 (173) +26
Northern Hemisphere - 1   Southern Hemisphere - <1

Epsilon Virginids (Non-IMO Shower)  13:28 (202) +09
Northern Hemisphere - <1   Southern Hemisphere - <1

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#2007

Clear Skies!
Robert Lunsford
American Meteor Society