Meteor Activity Outlook for December 17-23, 2011

During this period the moon reaches it last quarter phase on Sunday December
18th. The half illuminated moon is still very bright and must be kept out of
your field of view for successful meteor observations. During this period, the
evening hours, which are unfortunately much less active with meteors, will be
completely free of any interfering moonlight. As the week progresses the moon
will wane in phase and will rise approximately forty-five minutes later with
each passing night. With this scenario, viewing conditions during the more
active morning hours will improve with each passing night. The estimated total
hourly rates for evening observers this week is near five as seen from the
northern hemisphere and three as seen from the southern hemisphere. For morning
observers the estimated total hourly rates should be near twelve two as seen
from mid-northern latitudes and eight from mid-southern latitudes. 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 due to moonlight.

The radiant (the area of the sky where meteors appear to shoot from) positions
and rates listed below are exact for Saturday night/Sunday morning December
17/18. 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 particles produced by comet 2P/Encke are no longer encountering the
Earth, the Taurid showers for 2011 are over and we resume reporting activity
from the Antihelion (ANT) 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 prograde 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 a 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 06:36 (099)
+23. This position lies in western Gemini, three
degrees southwest of the third magnitude star Epsilon Geminorum. Antihelion
activity may also appear from eastern Taurus, northeastern Orion, or southern
Auriga. This radiant is best placed near midnight local standard time (LST),
when it lies on the meridian and is located highest in the sky. Rates at this
time should be near two per hour as seen from the northern hemisphere and one
per hour from south of the equator. With an entry velocity of 30 km/sec., the
average Antihelion meteor would be of slow velocity.

The last of the Monocerotids (MON) may be seen this weekend from a radiant
located at 07:03 (106) +07. This position lies on the Monoceros/Canis Minor
border, ten degrees west of the brilliant zero magnitude star Procyon (Alpha
Canis Minoris). Rates would be less than one per hour no matter your location.
The Monocerotids are best seen near 0100 LST when the radiant lies highest above
the horizon. At 41 km/sec. the Monocerotids produce mostly meteors of medium
velocity.

The last of the Sigma Hydrids (HYD) may be seen this weekend from a radiant
located at 08:54 (134) +00. This position lies in western Hydra, five degrees
south of the third magnitude star Zeta Hydrae. Rates would be less than one per
hour no matter your location. The Sigma Hydrids are best seen near 0300 LST when
the radiant lies highest above the horizon. At 61 km/sec. the Sigma Hydrids
produce mostly swift meteors.

The December Leonis Minorids (DLM) are active from a radiant located at 10:39
(160) +31. This position lies in eastern Leo Minor, ten degrees northeast of the
third magnitude star Zeta Leonis. These meteors are best seen near 0500 LST when
the radiant lies highest above the horizon. This shower peaks on December 20th
so current rates would be near one 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.

The Coma Berenicids (COM) are active from a radiant located at 11:51 (178) +18.
This position actually lies in eastern Leo, two degrees north of the second
magnitude star Denebola (Beta Leonis). These meteors are best seen near 0600 LST
when the radiant lies highest above the horizon. This shower peaked on December
16th so current rates would be near one per hour no matter your location. This
week will be your only opportunity to see these meteors as the shower will be
over by the 23rd. At 65 km/sec. the Coma Berenicids produce mostly swift
meteors.

Activity from the Ursids (URS) may begin to appear this weekend from a radiant
located at 13:58 (210) +76. This position lies in eastern Ursa Minor, fifteen
degrees east of the second magnitude star Kochab (Beta Ursa Minoris). It must be
remembered that the length of degrees are smaller in high declinations so the
radiant is actually closer to this star than these figures inply. These meteors
are best seen during the last dark hour before dawn, when the radiant lies
highest above the horizon in a dark sky. This shower is not well seen from the
southern hemisphere. Maximum activity is not expected until Friday December
23th, so current hourly rates would probably be less than one. On the morning of
maximum, hourly rates of between 5-10 Ursids may be seen. At 33 km/sec. the
Ursids produce mostly medium-slow meteors.

As seen from the mid-northern hemisphere (45N) one would expect to see
approximately eight sporadic meteors per hour during the last hour before dawn
as seen from rural observing sites. Evening rates would be near three per hour.
As seen from the mid-southern hemisphere (45S), morning rates would be near five
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. Morning rates are reduced 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.