Meteor Activity Outlook for December 14-20, 2007

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.