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 13. 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.
Unfortunately this year the bright moon spoils the show during the first week of
the month. During the second week of December the moon will pass its last quarter
phase and will not be such a nuisance .
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 full phase
on Thursday December 31st. On that date the moon lies opposite the sun and is in
the sky the entire night. This weekend the waxing gibbous moon sets during the
early morning hours allowing a couple of hours of viewing in dark conditions
before the onset of morning twilight. The estimated total hourly rates for evening
observers this week is near three no matter your location. For morning observers
the estimated total hourly rates should be near twenty from the northern hemisphere
and fifteen as seen from the southern hemisphere. 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. Rates are reduced
this week due to moonlight.
The radiant positions and rates listed below are exact
for Saturday night/Sunday morning December 26/27. 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:
Now that the activity from particles produced by comet 2P/Encke has ceased encountering
the Earth, the Taurid showers for 2009 are over and we resume reporting activity from
the Antihelion radiant. This is not a true radiant but rather activity caused
by the Earth’s motion through space. As the Earth revolves around the sun it encounters
particles orbiting in a pro-grade motion that are approaching their perihelion point.
They all appear to be radiating from an area near the opposition point of the sun,
hence the name Antihelion. These were once recorded as separate showers throughout the
year but it is now suggested to bin them into their category separate from true
showers and sporadics. This radiant is a very large oval some thirty degrees wide
by fifteen degrees high. Activity from this radiant can appear from more than one
constellation. The position listed here is for the center of the radiant which is
currently located at 07:12 (108) +22. This position lies in central Gemini, two
degrees west of the fourth magnitude star Delta Geminorum. Since the radiant is
so large, Antihelion activity may also appear from eastern Taurus, northeastern
Orion, western Cancer, or southern Auriga. This radiant is best placed near 0100
local standard time (LST) when it lies on the meridian and is highest in the sky.
Rates at this time should be near three per hour as seen from the northern hemisphere
and two per hour from south of the equator. With an entry velocity of 30 km/sec.,
the average Antihelion meteor would be of slow speed.
Activity from the Alpha Hydrids (AHY) begin to appear on the morning of
December 30th. This shower reaches maximum activity on the 31st from a radiant
located at 08:24 (126) -08. This position lies in extreme western Hydra, fifteen
degrees west of the second magnitude star Alphard (Alpha Hydrae). These meteors
are best seen near 0200 LST when the radiant lies highest above the horizon. Due
to the intense moonlight present at maximum, hourly rates from this shower will
be less than one per hour no matter your location. At 45 km/sec. the Alpha Hydrids
produce meteors of medium velocity.
The December Leonis Minorids (DLM) are active from a radiant located at 11:10
(168) +27. This position lies in a blank area of the sky where the borders of Leo
Minor, Leo, and Ursa Major meet. The nearest bright stars are Nu and Xi Ursae Majoris
which lie five degrees to the northeast. These meteors are best seen near 0500 LST
when the radiant lies highest above the horizon. This shower peaked on December
20th so current rates would be near two per hour as seen from the northern hemisphere
and less than one per hour as seen from south of the equator. At 64 km/sec. the
December Leonis Minorids produce mostly swift meteors.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately
fifteen Sporadic meteors per hour during the last hour before dawn as seen
from rural observing sites. Evening rates would be near two per hour. As seen from
the mid-southern hemisphere (45S), morning rates would be near twelve per hour as
seen from rural observing sites and two per hour during the evening hours. Locations
between these two extremes would see activity between the listed figures. Sporadic
rates are reduced this week due to moonlight.
The table below presents a condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning but may be used
all week long.
| SHOWER | DATE OF MAXIMUM ACTIVITY | CELESTIAL POSITION | ENTRY VELOCITY | CULMINATION | HOURLY RATE | CLASS* | RA (RA in Deg.) DEC | Km/Sec | Local Standard Time | North-South | Antihelion (ANT) | – | 07:12 (108) +22 | 30 | 01:00 | 3 – 2 | II | Alpha Hydrids (AHY) | Dec 31 | 08:24 (126) -08 | 45 | 02:00 | <1 - <1 | II | December Leonis Minorids (DLM) | Dec 20 | 11:10 (168) +27 | 64 | 05:00 | 2 – <1 | II |
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