(meteorobs) Meteor Activity Outlook for December 22-28, 2012

[Robert Lunsford]

During this period the moon reaches its full  phase on Friday December 28th. At this time the moon is located opposite the sun and will remain in the sky all night long. This weekend the waxing gibbous moon will set during the early morning hours and will allow several hours of dark sky viewing before dawn arrives. As the week progresses this window of dark skies shrinks until late in the week when the moon will remain above the horizon all night long. The estimated total hourly meteor rates for evening observers this week is near three for observers located at mid-northern latitudes and two for observers in mid-southern latitudes. For morning observers the estimated total hourly rates should be near twenty four from the mid-northern hemisphere and ten 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 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 22/23. 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:

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 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 06:56 (104) +22. This position lies in central Gemini, four degrees southeast of the third magnitude star Mebsuta (Epsilon Geminorum). Antihelion activity may also appear from eastern Taurus, northeastern Orion, Cancer, Canis Minor, Monoceros, or southern Auriga. This radiant is best placed near midnight local standard time (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 Leonis Minorids (DLM) are active from a radiant located at 10:52 (163) +30. This position lies in central Leo Minor, approximately four degrees southwest of the third magnitude star Alula Borealis (Nu Ursae Majoris). These meteors are best seen near 0400 LST when the radiant lies highest above the horizon. This shower peaked 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.

The Coma Berenicids (COM) are best seen from December 23 through January 2. Maximum activity occurs on January 1st when this shower is the fourth strongest in the sky. The current radiant position lies at 11:46 (176) +18. This position actually lies eastern Leo, four degrees northwest of the second magnitude star Denebola (Beta Leonis). Current hourly rates would most likely be less than one shower member per hour no matter your location. 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 Coma Berenicids would produce mostly swift meteors.

IMO Shower #247 seems to be a northern counterpart of the Coma Berenicids. It shares the same right ascension (celestial longitude) as the Coma Berenicids but is located nearly twenty degrees further north. The activity period is shorter than the Coma Berenicids as it is best seen from December 24-27, with maximum activity occurring on the 24th. Maximum rates would be near one per hour as seen from the northern hemisphere and less than one as seen from south of the equator. At maximum activity the radiant is located at 12:00 (180) +37, which is located in a remote area of southeastern Ursa Major. The nearest bright star would be third magnitude star Alula Borealis (Nu Ursae Majoris), which is located ten degrees to the southwest. 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 66 km/sec. IMO Shower #247  would produce mostly swift meteors.

Studies by Sirko Molau and Juergen Rendtel of the IMO discovered an active radiant in Virgo this time of year. The December Sigma Virginids (DSV) are 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. Current rates would most likely be less than one shower member no matter you location. The current radiant location is at 13:52 (208) +04 which place it in northern Virgo some four degrees northwest of the fourth magnitude star Tau 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.

The Ursids (URS) peak on the morning of December 22 from a radiant located at 14:32 (218) +75. This position lies in eastern Ursa Minor, just northeast of the second magnitude star Kochab (Beta Ursa Minoris). These meteors are best seen during the last dark hour before dawn, when the radiant lies highest above the horizon in a dark sky. Due to the extreme northerly location meteors from this shower are not visible from the southern hemisphere. On the morning of maximum, hourly rates of between 5-10 Ursids may be seen during the late morning hours. At 33 km/sec. the Ursids produce mostly medium-slow meteors.

The Quadrantids (QUA) begin to appear in weak numbers on the morning of December 26th. The radiant is then located near 15:04 (226) +53, which places it in northern Bootes, eight degrees southwest of the third magnitude star Edasich (Iota Draconis). Rates at this time would be less than one shower member per hour no matter your location. 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 42 km/sec. the Quadrantids would produce mostly meteors of medium velocity.

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 two 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 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 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) - 06:56 (104) +22   Velocity - 30km/sec.
Northern Hemisphere - 3 per hr.   Southern Hemisphere - 2 per hr

December Leonis Minorids (DLM) - 10:52 (163) +30   Velocity - 64km/sec.
Northern Hemisphere - 2 per hr.   Southern Hemisphere - <1 per hr

Coma Berenicids (COM) - 11:46 (176) +18   Velocity - 69km/sec.
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr

IMO #247  - 12:00 (180) +37   Velocity - 66km/sec.
Northern Hemisphere - 1 per hr.   Southern Hemisphere - <1 per hr

Dec. Sigma Virginids (DSV) - 13:52 (208) +04  Velocity - 44km/sec.
Northern Hemisphere - <1 per hr. Southern Hemisphere - <1 per hr

Ursids (URS) - 13:58 (210) +76   Velocity - 33km/sec.
Northern Hemisphere - 7 per hr. Southern Hemisphere - 0 per hr

Quadrantids (QUA) - 15:04 (226) +53    Velocity - 42km/sec.
Northern Hemisphere - <1 per hr. Southern Hemisphere - <1 per hr

Clear Skies!
Robert Lunsford
American Meteor Society