Meteor Activity Outlook for December 22-28, 2006

December is the last month of strong activity as seen in the northern hemisphere. During the first half of the month minor showers are active in the constellations of Taurus (Antihelions), Monoceros (Monocerotids), Puppis (Puppid-Velids), Hydra (Sigma Hydrids), and Leo (Coma Berenicids). Strong sporadic rates continue during the morning hours as long as the moon is below the horizon. Rates increase significantly with the arrival of the Geminids during the second week of the month. From the southern hemisphere, sporadic rates are increasing in strength toward a peak in January. Meteors from the above minor showers are also well seen from south of the equator. The Geminids also increase the southern activity, but not nearly to the extent that is witnessed in the northern hemisphere.

This week the moon reaches its first quarter phase on Wednesday December 27. At this time the moon will set near midnight, leaving the morning sky free of interfering moonlight. This weekend the waxing crescent moon will not be a factor as it will set well before midnight. The estimated total hourly rates for evening observers this week is near three for those located north of the equator and two for observers south of the equator. For morning observers the estimated total hourly rates should be near twenty for northern observers and eighteen for those located south of the equator. 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 due to moonlight.

The radiant positions listed below are exact for Saturday night/Sunday morning December 23/24. 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. This method 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.

These showers are expected to be active this week:

The Antihelion (ANT) radiant is now centered at 07:00 (105) +22. This area of the sky lies in central Gemini, four degrees west of the third magnitude star Delta Geminorum. This radiant is best placed near 0100 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 for observers located south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.

The Coma Berenicids (COM) peaked near December 20 with an average ZHR of five. The current location of this radiant is 12:00 (180) +23. This area of the sky is located on the Leo/Coma Berenices border some eight degrees northeast of the second magnitude star Denebola (Beta Leonis). This radiant is probably responsible for the many reports of activity in Leo during the month of December. 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. It appears that three percent of the total sporadic activity for the night is related to this radiant. At 62km/sec., the average meteor from this radiant would be swift.

The Ursids (URS) peak on December 23 with an average ZHR of ten. Peter Jenniskens mentions in his new book the possibility of a minor outburst of Ursids near 2000 Universal Time on December 22. This timing is during the afternoon hours for North America and favors the eastern hemisphere with the radiant being highest for the eastern Pacific area. Past outbursts have mostly been made up of faint meteors more suitable to intensified video cameras. Visual observers may not notice any extra activity. The location of this radiant is 14:28 (217) +74. This area of the sky is located in southern Ursae Minor, close to the orange second magnitude star Kochab (Beta Ursae Minoris). This area of the sky is circumpolar (never sets) for most of the northern hemisphere. While activity may be seen during the entire night, these meteors are best seen during the last dark hour before dawn when the radiant lies highest above the horizon. Due to the high northern declination (celestial latitude), this shower is not visible to observers located south of the equator. At 33 km/sec. the Ursids will usually produce meteors of medium to slow velocity. To read more on viewing the Ursid shower visit the AMS website at: http://www.amsmeteors.org/showers.html#ursids

Sporadic rates have reached the late year plateau for observers located in the northern hemisphere. One would expect to see perhaps fifteen random meteors during the last hour before dawn from rural observing sites. During the first dark hour after the end of evening twilight, perhaps three random meteors can be seen per hour. Sporadic rates increase as the night progresses so rates seen near midnight would be near ten per hour. Sporadic rates seen from the southern hemisphere have passed their annual minimum and are rising again. One would expect to see approximately thirteen random meteors per hour during the last hour before dawn and two per hour during the first dark hour after the end of evening twilight. Rates near midnight would be near eight per hour. Evening rates are reduced due to moonlight.