(meteorobs) Meteor Activity Outlook for December 12-18, 2015

[Robert Lunsford]

During this period the moon reaches its first quarter phase on Friday December 18th. On that date the moon will be located 90 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.  The estimated total hourly meteor rates for evening observers this week is near 10 as seen from mid-northern latitudes (45N) and 5 as seen from tropical southern locations (25S). For morning observers the estimated total hourly rates should be near 70 as seen from mid-northern latitudes (45N) and 30 as seen from tropical southern locations (25S). 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 12/13. 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 have ceased encountering the Earth, the Taurid showers for 2015 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 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 Anthelion. 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. There are several lists that have the Chi Orionids currently active, but we include them with the Anthelions as the celestial positions overlap. 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, just north of the two 4th magnitude stars known as Upsilon and Eta Geminorum. Anthelion activity may appear from eastern Taurus, northeastern Orion, southern Auriga as well as western Gemini. 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 3 per hour as seen from the northern hemisphere and less than 2 per hour from south of the equator. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.

The Monocerotids (MON) are active from a radiant located at 06:52 (103) +08. This position lies in northern Monoceros, 5 degrees south of the 3rd magnitude star known as Xi Geminorum. Current rates should be near 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) reach maximum activity on Monday morning December 14 when rates could exceed 100 per hour from dark sky sites. At that time the radiant is located near 07:33 (113) +32. This position lies in northern Gemini, just northwest of the 2nd magnitude star known as Castor (Alpha Geminorum). Rates this weekend should be very strong, but exact numbers depend on your latitude. The best locations are mid-northern latitudes down to the equator. Any further south than than and rates will decline due to the lower radiant altitude. At 34 km/sec. the Geminids produce mostly meteors of medium velocity. There should also be many Geminid fireballs visible Saturday through Tuesday.

The Sigma Hydrids (HYD) are active from November 26 through December 21, with maximum activity occurring on December 6. The radiant is currently located at 08:24 (126) +02, which places it in western Hydra, just west of the small circular group of stars that form the head of Hydra. These meteors are best seen near 0300 LST when the radiant lies highest above the horizon. Current rates should be near 3 per hour no matter your location. With an entry velocity of 61 km/sec., most activity from this radiant would be of swift speed.

The Eta Hydrids (EHY) were recently discovered by members of of the Croatian Meteor Network. This radiant is active from December 10-18 with maximum activity occurring on December 12. The radiant is currently located at 09:16 (139) +01 , which places it in western Hydra, 1 degree south of the 4th magnitude star known as Theta Hydrae. This position is close to the Sigma Hydrids so care must be taken to separate the two sources. These meteors are best seen near 0400 LST when the radiant lies highest above the horizon. Current rates should be near 1 per hour no matter your location. With an entry velocity of 63 km/sec., most activity from this radiant would be of swift speed.

The December Leonis Minorids (DLM) are a shower of long duration active from December 6th through January 18th. Maximum occurs near December 21st when rates may reach 3 an hour. During this period I would expect an hourly rates of near 1 from a radiant located at 10:08 (152) +35. This position lies in western Leo Minor, near the faint star known as 21 Leo Minoris. These meteors are best seen near 0400 LST when the radiant lies highest above the horizon. At 63 km/sec. the December Leonis Minorids produce mostly swift meteors. These meteors are not well seen from the southern hemisphere.

The Psi Ursa Majorids (PSU) were discovered by the Japanese observers using data from SonotaCo. These meteors are active from December 1-16 with maximum occurs on December 4th. The radiant located at 11:44 (176) +42, which places it 7 degrees southeast of the 3rd magnitude star known as Psi Ursae Majoris. These meteors are best seen near 0400 LST when the radiant lies highest above the horizon. Rates would most likely be less than 1 per hour. At 63 km/sec. the Psi Ursa Majorids produce mostly swift meteors.

The December Chi Virginids (XVI) was discovered by Japanese observers using the data of SonotaCo. This source is active from December 8-24 with maximum activity occurring on the 17th . The current radiant location is at 12:36 (189) -10, which places it in west-central Virgo. This is a rather blank part of the sky. The easiest way to find the radiant is to draw a line between Porimma (Gamma Virginis) and Algorab (Alpha Corvi). Half-way between these two fairly bright stars is close to the radiant. Note the faint star 21 Virginis also lies close to this radiant. Note that the position given in last week's outlook is incorrect. Current rates would most likely be near 1 shower member no matter you 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 December Chi Virginids would produce mostly swift meteors.

The December Sigma Virginids (DSV) was discovered by John Greaves using the data of SonotaCo. IMO video cameras confirmed that this source is active during most of December and into the first week of January. Visual observers have their best chance at catching these meteors from December 17-31. Peak rates occur near December 24th. The current radiant location is at 13:00 (195) +06 which places it in northern Virgo some 3 degrees northeast of the 3rd magnitude star known as Auva (Delta Virginis). Current hourly rates would be less than 1 shower member no matter you 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 68 km/sec. the December Sigma Virginids would produce mostly swift meteors.

The December Alpha Draconids (DAD) were discovered by the Japanese observers using data from SonotaCo and is active from December 5-18. They were predicted to peak on December 7th. The radiant is currently located at 13:52 (208) +58. This position actually lies in northeastern Ursa Major, 5 degrees northeast of the second magnitude star known as 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. Current rates would most likely be less than 1 per hour no matter your location. Recent analysis by the IMO has revealed that this shower actually has two activity periods. The one listed above and another lasting from December 26-January 1st.

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 4 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 7 per hour as seen from rural observing sites and 3 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.

 
Anthelion (ANT) -  06:16 (094) +23  Velocity - 30km/sec. 
Northern Hemisphere - 3 per hr.   Southern Hemisphere - 2 per hr 
 
Monocerotids (MON) - 06:52 (103) +08  Velocity - 41km/sec. 
Northern Hemisphere - 1 per hr.   Southern Hemisphere - 1 per hr 
 
Geminids (GEM)  - 07:33 (113) +32  Velocity - 34km/sec. 
Northern Hemisphere - 50 per hr.   Southern Hemisphere - 25 per hr 
 
Sigma Hydrids (HYD)  -  08:24 (126) +02  Velocity - 61km/sec. 
Northern Hemisphere - 3 per hr.   Southern Hemisphere - 3 per hr 
 
Eta Hydrids (EHY)  -  09:16 (139) +01  Velocity - 63km/sec. 
Northern Hemisphere - 1 per hr.   Southern Hemisphere - 1 per hr 
 
Dec. Leonis Minorids (DLM)  -  10:08 (152) +35  Velocity - 63km/sec. 
Northern Hemisphere - 1 per hr.   Southern Hemisphere - <1 per hr 
 
Psi Ursa Majorids (PSU)  -  11:44 (176) +42  Velocity - 61km/sec. 
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr 
 
Dec. Chi Virginids (XVI)  -  12:36 (189) -10  Velocity - 69km/sec. 
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr 
 
Dec. Sigma Virginids (DSV)  -  13:00 (195) +06  Velocity - 68km/sec. 
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr 
 
Dec. Alpha Draconids (DAD)  -  13:52 (208) +58  Velocity - 41km/sec. 
Northern Hemisphere - 1 per hr.   Southern Hemisphere - <1 per hr 
 
Clear Skies! 
Robert Lunsford 	 
American Meteor Society