The moon reaches its last quarter phase on Friday December 27. At this time the moon will rise near midnight and be present in the morning sky for the remainder of the night. As the week progresses the waning moon will be less of a problem as it becomes thinner and moves closer to the sun. The estimated total hourly rates for evening observers this week should be near 3 for everyone regardless of location. For morning observers the estimated total hourly rates should be near 12 for those located in the Northern Hemisphere and 10 for those in the Southern Hemisphere. These rates assume that you are watching from rural areas away from all sources of light pollution. 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. Lunar interference reduces the morning activity this week.
The positions listed below are exact for Saturday night/Sunday morning December 28/29. The positions do not change greatly day to day so these positions may be used during this entire period. Most star atlases (available at science stores and libraries) 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 location. Meteor activity is not seen from radiants that are located below the horizon. The radiants below are listed in a west to east manner in order of right ascension (celestial longitude). The radiants listed first are located further west therefore are accessible earlier in the night while those listed last rise later in the night. This list also provides the order of ascending velocity for each radiant with those listed first usually being much slower than those last on the list. Velocity should not be the prime factor for shower association as all showers can produce slow meteors. Slow meteors can be produced from normally swift showers, such as the Leonids, when meteors appear near the radiant or close to the horizon. The true velocity is only revealed in shower members seen far from the radiant and high in the sky.
The Antihelion source is now centered at 07:28 (112) +22. This area of the sky is located in eastern Gemini, 3 degrees east of the 3rd magnitude star Delta Geminorum. Since this source is large and diffuse, any slow to medium speed meteor from western Cancer or eastern Gemini could be a candidate for this shower. The area of the sky is best placed near 0100 local standard time when it lies on the meridian and is highest in the sky. At this time expect to see 3 shower members per hour from locations north of the equator and 1 per hour for sites south of the equator.
Unlike most
of the annual showers the antihelion source is produced by debris from unknown
objects orbiting in a direct motion like the earth. These objects are most
likely asteroids, which produce stony and metallic debris whose density is
much greater than material produced by comets. This debris collides with
the earth on the inbound portion of its orbit, before its closest approach
to the sun. Therefore we best see them just after midnight when we are facing
the direction from which this activity appears. The antihelion source is active
all year from an area of the sky nearly opposite that of the sun. The center
of this source will move approximately one degree eastward per day and travels
through many different constellations over the course of a year. It may
make sense to list these meteors as antihelions or "ANT" but
a majority of meteor organizations prefer that you list them from the constellation
in which the radiant is currently located or the constellation where the
shower reaches maximum activity. Those who share their reports with the I.M.O.
should call these meteors Delta Cancrids or "DCA" after
December 31.
The Northern Apex source is now centered at 12:28 (187) +12. This position lies in northwestern Virgo, midway between the 2nd magnitude Denebola (Beta Leonis) and the 3rd magnitude star Vindemiatrix (Epsilon Virginis). This area of the sky is best placed for viewing during the last dark hour before dawn. Since this source is large and diffuse any meteors from southern Coma Berenices or northwestern Virgo could be a good candidate for this shower. This source should provide at least 2 meteors per hour for those in the Northern Hemisphere and 1 per hour for those in the Southern Hemisphere.
Like the antihelion source both apex areas are active all year long and travel approximately one degree eastward per day. Unlike the antihelion debris these particles orbit the sun in a retrograde motion opposite that of the earth and are most likely produced by unknown comets. They strike the earth after their closest approach to the sun. Since they are moving in opposite directions these particles strike the earth at tremendous velocities often creating bright meteors with persistent trains. These particles strike the earth on the morning side of earth and are best seen just before morning twilight while the sky is still perfectly dark. There are meteors with a zero inclination that radiate precisely from the apex point on the ecliptic, exactly 90 degrees west of the sun. These meteors are rare though as the earth orbits the sun it "sweeps clean" much of the material that shares the same orbit. Much more debris is located just north and south of the earth's orbit with slightly higher or lower inclinations. This creates the northern and southern branches of the apex activity. Meteors from both branches are normally included in the sporadic count but could also be noted in some manner as to which branch of the apex complex they appear to radiate. Those who report to the I.M.O. should label these meteors as Coma Berenicids or COM.
The Southern Apex
source lies exactly 30 degrees south of its northern counterpart at 12:28 (187) -18. This position lies only 1 degree south of
the 3rd magnitude star Delta Corvi. Like the northern apex, these meteors
are best seen toward dawn when the radiant lies highest above the horizon
in a dark sky. Any meteor from Corvus or southern Virgo could a candidate
from this source. Rates should be near 2 per hour from the Southern Hemisphere
and 1 per hour from the Northern Hemisphere.
The Sporadic rates for the Northern Hemisphere are now slowly declining and will do so until June. One would currently expect to see perhaps 6 random meteors per hour during the last hours before dawn from rural observing sites. This estimate and the morning estimate for the Southern Hemisphere does not include the apex meteors listed above. During the evening hours perhaps 3 random meteors can be seen per hour from the Northern Hemisphere. Rates seen from the Southern Hemisphere are equal to those seen in the northern skies with perhaps 6 random meteors being seen per hour during the early morning hours and 3 per hour during the evening. Lunar interference reduces the morning activity this week.
Clear Skies!