Meteor Activity Outlook for December 31, 2011 to January 6, 2012

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.

January is best known for the Quadrantids, which have the potential of being the best shower of the year. Unfortunately this shower is short lived and occurs during some of the worst weather in the northern hemisphere. Due to the high northern declination (celestial latitude) and short summer nights, little of this activity can be seen south of the equator. Sporadic rates are generally similar in both hemispheres this month. Sporadic rates are falling though for observers in the northern hemisphere and rising as seen from the southern hemisphere.

During this period the moon reaches it first quarter phase on Sunday January 1st. At this time the moon will be located ninety degrees east of the sun and will set near midnight local standard time (LST). As the week progresses the waxing gibbous moon will set later in the morning hours, shrinking the window of opportunity to view under a dark sky. The estimated total hourly rates for evening observers this week is near three as seen from the northern hemisphere and two as seen from the southern hemisphere. For morning observers the estimated total hourly rates should be near fifteen as seen from mid-northern latitudes and ten from mid-southern latitudes. 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 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 31st/January 1st. 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:

The large Antihelion (ANT) radiant is currently located at 07:32 (113) +21. This position lies in eastern Gemini, two degrees east of the fourth magnitude star Wasat (Delta Geminorum). Due to the large size of this radiant, Antihelion activity may also appear from Monoceros, Canis Minor, or Cancer. This radiant is best placed near 0100 LST, when it lies on the meridian and is located highest in the sky. Rates at this time should be near two per hour as seen from the northern hemisphere and one 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 Alpha Hydrids (AHY) are active from December 31st through January 9th. Peak activity occurs on January 1st from a radiant located at 08:24 (126) -08. This position lies in extreme western Hydra, fifteen degrees west of the second magnitude star Alphard (Alpha Hydrae). Rates would most likely be near one per hour, no matter your location. The Alpha Hydrids are best seen near 0200 LST when the radiant lies highest above the horizon. At 45 km/sec. the Alpha Hydrids produce mostly meteors of medium velocity.

Studies of the IMO’s video database by Sirko Molau and Juergen Rendtel has shown another active radiant in Leo this time of year. The January Leonids (JLE) are active from January 1st to 6th with maximum activity occurring on January 2nd. On the 2nd the radiant is located at 09:46 (147) +24. This position lies in western Leo just west of the third magnitude star Algenubi (Epsilon Leonis). This is a very minor display with hourly rates of less than one expected, even at maximum activity. They are best seen near 0300 LST when the radiant lies highest above the horizon. At 54 km/sec. the January Leonids (JLE) produce mostly meteors of medium-swift velocity.

The December Leonis Minorids (DLM) are active from a radiant located at 11:27 (172) +25. This position lies in a blank area of northeastern Leo. The nearest bright star is third magnitude Zosma (Delta Leonis), which lies six degrees to the southwest. These meteors are best seen near 0500 local standard time (LST) when the radiant lies highest above the horizon. This shower peaked on December 20th so current rates would be near one 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 Quadrantids (QUA) or January Bootids are active from January 1st through the 10th. A sharp maximum is predicted to occur near 0730 Universal Time on the 4th. This corresponds to 02:30 EST and 23:30 PST (January 3rd). This is good timing for viewers located in eastern North America as the radiant will rising above the northeastern horizon. It would even be better if the maximum were a it later as the radiant would be located higher in the sky, producing more activity. Rates will depend on the exact time of maximum and whether the moon is still above the horizon. Assuming the 0730 UT timing is correct, the further one is located in North America, the better. Eastern observers may be able to see 60-75 Quadrantids per hour. If your skies are very clear and dark, allowing you to see faint meteors, your rates could top 100 per hour. Observers located in the western portions of North American will have lower rates but will also have the opportunity to see Quadrantid “earthgrazers”. Earthgrazers are meteors that skim the upper portion of the atmosphere therefore lasting much longer than normal and producing long trails in the sky. These meteors can only be seen when the radiant lies close to the horizon. As the radiant rises, the meteor paths will become shorter with shorter durations. Observers in the northern hemisphere outside of North America can expect to see a maximum of 25 Quadrantids per hour between moon set and dawn. Observers south of the equator will see little of this display as the radiant will have little chance to clear the horizon before morning twilight interferes.

At maximum the radiant is located at 15:21 (230) +49. This position lies in a barren  region of extreme northern Bootes, ten degrees northeast of the fourth magnitude star Beta Bootis. At 42 km/sec. the Quadrantids produce meteors of medium velocity. During exceptional activity some Quadrantid fireballs may be witnessed.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately ten 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.

Shower Name                 RA     DEC   Vel     Rates
                                         km/s   NH    SH
ANT Antihelions           07h 32m  +21    30     2     1
AHY Alpha Hydrids         08h 24m  -08    45     1     1
JLE January Leonids       11h 04m  +28    54    <1    <1
DLM Dec Leonis Minorids   11h 27m  +25    64     1    <1
QUA Quadrantids           15h 21m  +49    42    <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