The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.
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. Unfortunately this year the bright moon spoils the show during the first week of the month. During the second week of December the moon will pass its last quarter phase and will not be such a nuisance .
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 new phase on Wednesday December 16th. On that date the moon lies near the sun and cannot be seen at night. This weekend the waning crescent moon will rise during the late morning hours but will not cause any interference. The estimated total hourly rates for evening observers this week is near five as seen from the northern hemisphere and three from the southern hemisphere. For morning observers the estimated total hourly rates should be near forty from the northern hemisphere and twenty as seen from the southern hemisphere. 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 positions and rates listed below are exact for Saturday night/Sunday morning December 12/13. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.
The following showers are expected to be active this week.
Now that the activity from particles produced by comet 2P/Encke has ceased encountering the Earth, the Taurid showers for 2009 are over and we resume reporting activity from the Antihelion 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 pro-grade 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 their 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 06:16 (094) +23. This position lies in western Gemini near the fourth magnitude star Eta Geminorum. Antihelion activity may also appear from eastern Taurus, northeastern Orion, or southern Auriga. This radiant is best placed near 0100 local standard time (LST) when it lies on the meridian and is highest in the sky. Rates at this time should be ~3 per hour as seen from the northern hemisphere and ~2 per hour from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow speed.
The Monocerotids (MON) are active from a radiant located at 06:52 (103) +07. This position lies in northwestern Monoceros halfway between the bright stars Betelgeuse (Alpha Orionis) and Procyon (Alpha Canis Minoris). This shower peaked on December 8, so activity is waning. Current rates would most likely average < 1 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 Geminids (GEM) are active from a radiant located at 07:33 (113) +32. This position lies in northern Gemini near the fourth magnitude star Rho Geminorum. Although Geminid meteors can be seen all night long, they are best seen near 0200 LST when the radiant lies highest above the horizon. This shower is expected to peak Sunday and Monday December 13/14 when rates can surpass 60 shower members per hour as seen from dark sites. Geminid activity can be seen from the southern hemisphere but at at much reduced rate. As seen from south of the equator, Geminid activity could only be seen for a few hours before and after 0200 LST. At 35 km/sec. the Geminids produce mostly meteors of medium velocity.
The Puppid-Velids (PUP) are 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 10. 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 08:26 (126) -45. This position lies in western Vela, five degrees northeast of the second magnitude star Gamma Velorum. Peak rates occurred near December 7 so current activity is waning. These meteors are best seen near 0300 LST when the radiant lies highest above the horizon. 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 medium velocity.
Sigma Hydrids (HYD)
The Sigma Hydrids (HYD) are active from a radiant located at 08:42 (130) +01. This position lies in western Hydra, just below the group of fourth magnitude stars that make up the “head” of the water serpent. These meteors are best seen near 0300 LST when the radiant lies highest above the horizon. Current rates would be ~1 per hour no matter your location. At 61 km/sec. the Sigma Hydrids produce mostly swift meteors.
December Leonis Minorids (DLM)
The December Leonis Minorids (DLM) are active from a radiant located at 10:22 (155) +34. This position lies in central Leo Minor, approximately ten degrees north 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 ~1 per hour as seen from the northern hemisphere and < 1 per hour as seen from south of the equator. At 64 km/sec. the December Leonis Minorids produce mostly swift meteors.
Coma Berenicids (COM)
Activity from the Coma Berenicids (COM) has just begun for 2009. The radiant is located at 11:30 (173) +18. This position actually lies in eastern Leo, five degrees northwest 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 peaks on December 16th so current rates would be ~1 per hour no matter your location. At 65 km/sec. the Coma Berenicids produce mostly swift meteors.
December Alpha Draconids (DAD)
Lastly, the December Alpha Draconids (DAD) are active from a radiant located at 14:00 (210) +58. This position actually lies in northeastern Ursa Major, six degrees northeast of the second magnitude double star Mizar (Zeta Ursae Majoris). 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 near the end of its activity period so expected rates would be < 1 no matter your location. At 44 km/sec. the Alpha Draconids produce mostly medium speed meteors.
As seen from the mid-northern hemisphere (45N) one would expect to see ~16 Sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be ~3 per hour. As seen from the mid-southern hemisphere (45S), morning rates would be ~10 per hour as seen from rural observing sites and ~2 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 but may be used all week long.
Shower Name RA DEC Vel Rates km/s NH SH ANT Antihelions 06h 16m +23 30 3 2 MON Monocerotids 06h 52m +07 41 <1 <1 GEM Geminids 07h 33m +32 35 60 20 PUP Puppids-Velids 08h 26m -45 40 <1 2 HYD Sigma Hydrids 08h 42m +01 61 1 1 DLE Dec Leonis Minorids 10h 22m +34 64 1 <1 COM Coma Berenicids 11h 30m +18 65 1 1 DAD Dec Alpha Draconids 14h 00m +58 44 <1 <1 RA - Right Ascension DEC - Declination Vel - Velocity relative to Earth (in km per sec) Rates - Rate of visible meteors per hour from a dark site NH - Northern Hemisphere SH - Southern Hemisphere