Meteor Activity Outlook for December 19-25, 2015

During this period the moon reaches its full phase on Friday December 25th. On that date the moon will be located opposite the sun and will lie above the horizon all night long as seen from mid-northern latitudes. This weekend the waxing gibbous moon will set during the early morning hours, allowing a few hours of viewing under dark skies before the beginning of morning twilight. This window of opportunity shrinks with each passing night 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 3 as seen from mid-northern latitudes (45N) and 2 as seen from tropical southern locations (25S). For morning observers the estimated total hourly rates should be near 18 as seen from mid-northern latitudes (45N) and 14 as seen from tropical southern locations (25S). Evening rates are reduced during this period due to interfering moonlight. 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 19/20. 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 06:44 (101) +23. This position lies in central Gemini, just south of the 3rd magnitude stars known as Mebsuta (Epsilon Geminorum). Anthelion activity may appear from eastern Taurus, northeastern Orion, southern Auriga, Monoceros, Canis Minor, and western Cancer as well as 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 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.

The last of the Sigma Hydrids (HYD) are expected this weekend from a radiant located at 09:01 (135) +00. This area of the sky lies in westrn Hydra, 3 degrees southwest of the 4th magnitude star known as Theta Hydrae. These meteors are best seen near 0300 LST when the radiant lies highest above the horizon. Current rates should be less than 1 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 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. The radiant is currently located at 10:48 (162) +30. This position lies in southeastern Leo Minor, just south of the faint star known as 42 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 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 13:00 (195) -10, which places it in west-central Virgo. This position lies 5 degrees northwest of the bright 1st magnitude star known as Spica (Alpha Virginis). 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 13:24 (201) +05, which places it in northern Virgo some 5 degrees northeast of the 3rd magnitude star known as Auva (Delta Virginis). Current hourly rates should be near 1 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 68 km/sec. the December Sigma Virginids would produce mostly swift meteors.

Activity from the Ursids (URS) should begin to appear during the late-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 Tuesday 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 but the nearly full moon will interfere greatly. At 30 km/sec. the Ursids produce mostly medium-slow meteors.

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 2 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 1 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Moonlight interferes with evening rates during this period.