The following is a slightly edited version of Bob Lunsford’s excellent weekly summary of meteor activity. The original version 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. This activity will be tempered by a bright moon during the first week of the month. The next two weeks are moon-free and offer the meteor observer ample opportunities to view some celestial fireworks. 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. Much of the activity mentioned above can also be seen from the southern hemisphere. While the sporadic rates are not as strong as those seen from the north, they are stronger than the previous months and heading for a maximum in February. The warm, but short summer nights south of the equator make for some great viewing as long as the moon does not interfere.
During this period the moon reaches its first quarter phase on Wednesday December 19th. At this time the moon is located ninety degrees east of the sun and will set near midnight local standard time (LST). This weekend the waxing crescent moon will set during the early evening hours and will not cause any problems to meteor observers. As the week progresses the moon will set later and later, but will still allow unhampered views of the more active morning sky. The estimated total hourly meteor rates for evening observers this week is near four for observers located at mid-northern latitudes and three for observers in mid-southern latitudes. For morning observers the estimated total hourly rates should be near thirty from the mid-northern hemisphere and sixteen from the mid-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. Rates are slightly reduced during the evening hours during this period due to moonlight.
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 15/16. 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 2012 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 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 06:28 (097) +23. This position lies in western Gemini near the third magnitude star Mebsuta (Epsilon Geminorum). Antihelion activity may also appear from eastern Taurus, northeastern Orion, or southern Auriga. This radiant is best placed near midnight 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 from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.
The December Monocerotids (MON) are active from December 7th through the 18th. Peak activity occurred on December 8th so current rates should be less than one per hour no matter your location. The radiant is located at 07:00 (105) +07. This position lies in eastern Monoceros, ten degrees east of the zero magnitude star Procyon (Alpha Canis Minoris). 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) reached maximum activity on Thursday evening/Friday morning December 13/14. This weekend will be your last good opportunity to see any Geminids in 2012 as activity ceases next week. The radiant is currently located at 07:40 (115) +32, which places it in northeastern Gemini, just east of the second magnitude star Castor (Alpha Geminorum). Rates this weekend, when the radiant lies high in the sky, would be 20-40 per hour (depending on your viewing conditions) on the night of 14/15 and 10-20 per hour on the night of 15/16. Geminid meteors strike the atmosphere at 35km/sec, which will produce meteors of medium-slow velocity.
The Sigma Hydrids (HYD) are active from November 26 through December 20. Maximum activity occurred on December 6, so current rates would be near one per hour no matter your location. The radiant is located at 08:47 (132) +01. This position lies in western Hydra, just south of 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. At 61 km/sec. the Sigma Hydrids produce mostly swift meteors.
The December Leonis Minorids (DLM) are active from a radiant located at 10:32 (158) +32. This position lies in central Leo Minor, approximately ten degrees northeast 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 17th 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.
On the nights of December 19-21, weak activity from the Rho Leonids (RLE) may be noticed. Sirko Molau and Juergen Rendtel of the IMO have found the actual activity range is December 17-23, but away from the nights mentioned above, the display is very weak. Previous radiants for this shower were further north. Video results give a position at maximum near 10:34 (159) -05. This actually places it in central Sextans, some fifteen degrees southeast of the first magnitude star Regulus (Alpha Leonis). Rates could approach one shower member per hour during the last few hours before dawn on the nights previously mentioned. At 69 km/sec. the Rho Leonids would produce mostly swift meteors.
On the nights of December 15/16 and 16/17, weak activity from the Virgo/Corvus border may be noticed. This currently unnamed source is active from December 5-27, but incredibly weak except for the two nights mentioned above. The exact radiant position for IMO Shower #239 is 12:52 (193) -11. This places it some ten degrees west of the first magnitude star Spica (Alpha Virginis). At 70 km/sec. These meteors are best seen during the last dark hour before dawn, when the radiant lies highest above the horizon in a dark sky. IMO Shower #239 would produce mostly swift meteors.
Another shower found by Sirko Molau and Juergen Rendtel of the IMO are the December Sigma Virginids (DSV). This radiant is active through most of December and the first week of January. Visual observers have their best chance at catching these meteors from December 17 through January 1st. Maximum activity occurs on December 31st. The current radiant location is 13:32 (203) +05, which places it in northern Virgo some five degrees north of the third magnitude star Heze (Zeta Virginis). These meteors are best seen during the last dark hour before dawn, when the radiant lies highest above the horizon in a dark sky. At 69 km/sec. the December Sigma Virginids would produce mostly swift meteors.
Activity from the Ursids (URS) should begin to appear during the mid-week period from a radiant located at 13:58 (210) +76. This position lies in eastern Ursa Minor, fifteen degrees east of the second magnitude star Kochab (Beta Ursa Minoris). It must be remembered that the length of degrees are smaller in high declinations so the radiant is actually closer to this star than these figures imply. 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 not expected until Saturday December 22th, so current hourly rates this week 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.
Lastly, the December Alpha Draconids (DAD) are active from December 4-16. Maximum activity occurred on December 5. The radiant is currently located at 14:08 (212) +57. This position actually lies in northeastern Ursa Major, ten 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 not well seen from the southern hemisphere. Expected hourly rates would be less than one 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 approximately eleven 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. Evening rates are slightly reduced due to moonlight.
The list below presents a condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning.
Antihelions (ANT) – 06:28 (097) +23 Velocity – 30km/sec.
Northern Hemisphere – 3 per hr. Southern Hemisphere – 2 per hr
Dec. Monocerotids (MON) – 07:00 (105) +07 Velocity – 41km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – <1 per hr
Geminids (GEM) -07:40 (115) +32 Velocity – 35km/sec.
Northern Hemisphere – 10 per hr. Southern Hemisphere – 5 per hr
Sigma Hydrids (HYD) -08:47 (132) +01 Velocity – 61km/sec.
Northern Hemisphere – 1 per hr. Southern Hemisphere – 1 per hr
December Leonis Minorids (DLM) – 10:32 (158) +32 Velocity – 64km/sec.
Northern Hemisphere – 2 per hr. Southern Hemisphere – <1 per hr
Rho Leonids (RLE) – 10:34 (159) -05 Velocity – 69km/sec.
Northern Hemisphere – 1 per hr. Southern Hemisphere – 1 per hr
IMO #239 – 12:52 (193) -11 Velocity – 69km/sec.
Northern Hemisphere – 2 per hr. Southern Hemisphere – <1 per hr
Dec. Sigma Virginids (DSV) – 13:32 (203) +05 Velocity – 44km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – <1 per hr
Ursids (URS) – 13:58 (210) +76 Velocity – 33km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – <1 per hr
December Alpha Draconids (DAD) – 14:08 (212) +57 Velocity – 44km/sec.
Northern Hemisphere – <1 per hr. Southern Hemisphere – <1 per hr
Clear Skies!
Robert Lunsford
American Meteor Society
The Transient Sky - Comets, Asteroids, Meteors 