Meteor Activity Outlook for December 6-12, 2008

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.

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 Friday December 12th. At this time the moon will be in the sky all night long, overpowering the fainter meteors. This weekend the waxing gibbous moon will set during the early morning hours allowing several hours of dark sky viewing before the onset of morning twilight. The estimated total hourly rates for evening observers this week is near four for those located in the mid-northern hemisphere (45 N) and two for those viewing 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 twenty for those viewing from the mid-southern hemisphere (45 S). Locations between these two extremes would see activity between the listed figures. 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 the bright moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning December 6/7. 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 Phoenicids (PHO) are a periodic shower that rarely produces noticeable activity. The only impressive display produced by this shower occurred in 1956 when ZHR's were near 100. Peak activity occurs on December 6. Little activity is expected away from the peak night. The radiant is currently located at 01:16 (019) -53. This position lies in southeastern Phoenix some four degrees northwest of the bright zero magnitude star Achernar (Alpha Eridani). These meteors are best seen near 2100 (9pm) local standard time (LST, regardless of time zone) when the radiant lies highest above the horizon in a dark sky. Due to the southerly declination of the radiant, this shower is not visible north of the northern tropical areas. The deep southern hemisphere has the best chance of seeing any activity. At 22 km/sec. the Phoenicids produce very slow meteors.

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 05:44 (086) +23. This position lies in eastern Taurus, six degrees southeast of the second magnitude star El Nath (Beta Tauri). This area of the sky is best placed on the meridian near 0100 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.

Monocerotid (MON) activity begins and peaks this weekend. The radiant is located at 06:32 (098) +09. This area of the sky is located in northern Monoceros, seven degrees northeast of the first magnitude star Betelgeuse (Alpha Orionis). These meteors are best seen near 0100 LST when the radiant lies highest above the horizon. The peak for the Monocerotids occurs on Sunday December 7th. Rates then slowly decline until the activity ceases near December 20th. This shower would be equally well seen from both hemispheres. Current rates are most likely near two per hour. At 42 km/sec. the Monocerotids produce meteors of average velocity. Do not confuse this radiant with the nearby November Orionids (located eight degrees north),the Antihelion radiant located fifteen degrees to the northwest, and the Geminids located twenty degrees to the northeast. One must face toward these radiants for any hope of properly classifying them.

Sirko Molau's study of video radiants has shown that there is an active radiant located in northeastern Orion this time of year. The radiant is currently located at 6:40 (100) +17. This position lies in that portion of the sky occupied by the second magnitude star Alhena (Gamma Geminorum). Current rates should be near one shower member per hour. These meteors are best seen near 0200 LST when the radiant culminates on the meridian. At 45 km/sec. the November Orionids (NOO) produce meteors of medium-swift velocity. This shower has a very similar radiant position with the better known and much more active Orionids (of October and early November). Last year I called these the Lambda Orionids, not knowing the IAU had already listed a designation for this shower.

Currently the Geminids (GEM) should be producing two meteors per hour from a radiant located at 07:00 (105) +33. This position lies in northwestern Gemini, eight degrees west of the second magnitude star Castor (Alpha Geminorum). Toward the end of the week rates should increase to near five per hour as seen from the northern hemisphere. These meteors are best seen near 0200 LST when the radiant lies highest above the horizon in a dark sky. At 35 km/sec. the Geminids produce mostly medium speed meteors.

The Puppid-Velids (PUP) is a vast complex of weak radiants located in the constellations of Puppis and Vela. Visual plots and photographic studies have revealed many radiants in this area during November and December. The combined strength of these radiants can produce a ZHR of ten. Actual hourly rates will be much less unless you happen to be observing from the deep Southern Hemisphere. The center of this activity is currently located at 08:08 (122) -45. This position lies in eastern Puppis, two degrees north of the second magnitude star Gamma Velorum. Peak rates occurred near December 6. These meteors are best seen near 0300 LST when the radiant lies highest above the horizon in a dark sky. Observers located in the Southern Hemisphere have an advantage viewing this shower as the radiant will rise higher into their sky allowing more activity to be seen. At 40 km/sec. the Puppid-Velids produce meteors of average velocity.

The Sigma Hydrids (HYD) are active from a radiant located at 08:12 (123) +03. This position lies in eastern Canis Minor, seven degrees southwest of the zero magnitude star Procyon (Alpha Canis Minoris). These meteors are best seen near 0400 LST when the radiant lies highest above the horizon in a dark sky. At 60 km/sec. the Sigma Hydrids produce mostly swift meteors.

Activity from the Coma Berenicids (COM) are just now beginning to appear. Hourly rateswould be less than one this week from a radiant located at 10:00 (150) +36. This area of the sky is located in central Leo Minor. The easiest way to pinpoint this area of the sky would be to look fifteen degrees north of the "sickle" of Leo. This radiant is probably responsible for the many reports of activity in Leo during the month of December. These meteors are best seen near 0500 LST when the radiant lies highest above the horizon. At 64 km/sec. the Coma Berenicids will usually produce meteors of swift velocity.

The Chi Virginids (CVR) were discovered during Sirko Molau's study of video radiants. Activity is first noticed on December 11th and the best rates occur a night later. The radiant is located at 12:20 (185) -08. This position lies in southwestern Virgo, eight degrees north of the third magnitude star Algorab (Delta Corvi). These meteors are best seen during the last dark hour before the start of morning twilight when the radiant lies highest above the horizon in a dark sky. At 69 km/sec. the Chi Virginids produce mostly swift meteors.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately sixteen 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 ten per hour as seen from rural observing sites and one per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Evening rates are reduced due to the bright moonlight.

The table below presents a summary of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning but may be used all week.