(meteorobs) Meteor Activity Outlook for Decemeber 20-26, 2014

[Robert Lunsford]

During this period the moon reaches its new phase on Monday December 22th. At this time the moon is located near the sun and cannot be seen at night. Later next week the waxing crescent moon will enter the evening sky but will pose no interference to meteor observers. The estimated total hourly meteor rates for evening observers this week is near 4 as seen from the northern hemisphere (45N) and 3 as seen from southern tropical latitudes (25S). For morning observers the estimated total hourly rates should be near 18 as seen from the northern hemisphere and 12 as seen from below the equator. 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. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.

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 20/21. 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.

These sources of meteoric activity 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 2014 are over and we resume reporting activity from the Anthelion (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 Anti-helion. 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 06:48 (102) +23. This position lies in central Gemini, 2 degrees south of the third magnitude star known as Mebsuta (Epsilon Geminorum). Anthelion activity may also appear from eastern Taurus, northeastern Orion, northern Monoceros, or southern Auriga. This radiant is best placed near 01:00 local standard time (LST) when it lies on the meridian and is highest in the sky. Rates at this time should be near 2 per hour as seen from the northern hemisphere and 1 per hour from south of the equator. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.

Weak activity from the Alpha Hydrids (AHY) may be seen later in this period. This shower was discovered by Dr. Peter Brown and other members of the Department of Physics and Astronomy, University of Western Ontario, London, Ontario Canada. They were using a meteoroid stream survey from the Canadian Meteor Orbit Radar to isolate radiants. This radiant is active from December 22 through January 7 with maximum activity occurring on December 31st. On Tuesday morning the radiant will be located at 07:52 (118) -05. This location lies in eastern Monoceros, 10 degrees southeast of the brilliant zero magnitude star known as Procyon (Alpha Canis Minoris).  This area of the sky is best placed near 0100 LST when the radiant lies highest above the horizon. Rates at this time should be less than 1 per hour no matter your location. With an entry velocity of 43 km/sec., the average Alpha Hydrid meteor would be of medium velocity.

The December Leonis Minorids (DLM) are active from December 6th through January 18th. The radiant is currently located at 10:50 (163) +30. This position lies in southeastern Leo Minor, 5 degrees southwest of the 3rd magnitude star known as Alula Borealis (Nu Ursae Majoris). These meteors are best seen near 0500 LST when the radiant lies highest above the horizon. This shower peaks on December 21st so rates would be near 3 per hour as seen from the northern hemisphere and 2 per hour as seen from south of the equator. At 63 km/sec. the December Leonis Minorids produce mostly swift meteors.

The December Chi Virginids (XVI) were discovered by members of SonotaCo based on video observations obtained in 2007 and 2008. This radiant is active from December 8-24 with maximum activity occurring on the 17th. The radiant is currently located at 13:02 (196) -10. This area of the sky is located in southern Virgo, 5 degrees northwest of the bright, 1st magnitude star known as Spica (Alpha Virginis). This area of the sky is best placed during the last hour before dawn when the radiant lies highest above the horizon in a dark sky. Rates would most likely be less than 1 per hour no matter your location. At 69km/sec., the average December Chi Virginid meteor would be swift.

The December Sigma Virginids (DSV) were discovered by John Greaves using data from SonotoCo. This radiant is active from December 6-31 with maximum occurring on the 24th. The current radiant location is 13:46 (206) +03, which places it in central Virgo, 3 degrees northeast 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. Current hourly rates would most likely be less than 1 no matter your location. At 68 km/sec. the December Sigma Virginids would produce mostly swift meteors.

The Ursids (URS) will peak on Monday morning from a radiant located at 14:32 (218) +75. This position lies in eastern Ursa Minor, close to the position occupied by the faint star known as 5 Ursae Minoris. The much brighter orange star known as Kochab (Beta Ursae Minoris) lies just a couple of degrees further away toward the southeast. 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 northern declination (celestial latitude), this shower is nearly invisible from the southern hemisphere.  On the morning of maximum, hourly rates of between 5-10 Ursids may be seen. At 30 km/sec. the Ursids produce mostly medium-slow meteors. Very little activity will be seen away from the night of maximum activity.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately 11 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 3 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 9 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 list below offers the information from above in a condensed form. Rates and positions are exact for Saturday night/Sunday morning except where noted in the shower descriptions.

Anthelion (ANT) - 06:48 (102) +23  Velocity - 30km/sec. 
Northern Hemisphere - 2 per hr.   Southern Hemisphere - 1 per hr. 
 
Alpha Hydrids (AHY) - 07:52 (118) -05  Velocity - 43km/sec. 
 Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr.

Dec. Leonis Minorids (DLM) - 10:50 (163) +30  Velocity - 63km/sec. 
Northern Hemisphere - 3 per hr.   Southern Hemisphere - 2 per hr. 
 
Dec. Chi Virginids (XVI) - 13:02 (196) -10  Velocity - 69km/sec. 
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr 
 
Dec. Sigma Virginids (DSV) - 13:46 (206) +03 Velocity - 68km/sec. 
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr 
 
Ursids (URS) - 14:32 (218) +75  Velocity - 30km/sec. 
Northern Hemisphere - 2 per hr.   Southern Hemisphere - <1 per hr 
  
Clear Skies! 
Robert Lunsford 	 
American Meteor Society