Meteor Activity Outlook for December 24-30, 2011

During this period the moon reaches it new phase on Saturday December 24th. At
this time the moon will be located near the sun and will be invisible at night.
As the week progresses the waxing crescent moon will enter the evening sky but
will not interfere with meteor observing as it is thin and will set long before
the active morning hours arrive. The estimated total hourly rates for evening
observers this week is near four 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 fifteen 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.

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
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. 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 07:04 (106)
+22. This position lies in central Gemini, four degrees west of the fourth magnitude star Wasat (Delta Geminorum). Antihelion
activity may also appear from Monoceros, northeastern Orion, Canis Minor, or
Cancer. 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 December Leonis Minorids (DLM) are active from a radiant located at 11:04
(166) +28. This position lies in eastern Leo Minor, six degrees northwest of the
third magnitude star Zosma (Delta Leonis). These meteors are best seen near 0500
local standard time (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.

The last of the Ursids (URS) may be seen this weekend from a radiant located at
14:40 (220) +75. This position lies in eastern Ursa Minor, two degrees north of
the second magnitude star Kochab (Beta Ursa Minoris). 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 on Friday December 23th, so hourly rates this
weekend 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
seven 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.

The table below presents a condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning.