The moon will reach its full phase on Thursday December 19. At this time the moon will be in the sky all night long as it rises near sunset and sets near sunrise. This weekend the waxing gibbous moon will set a few hours before the start of morning twilight. This will allow observers to get a short, but good glimpse of the Geminid activity this weekend. The estimated total hourly rates for evening observers this week should be near 3 for those in the Northern Hemisphere and 2 for those south of the equator. For morning observers the estimated total hourly rates should be near 25 for those located in the Northern Hemisphere and 15 for those located in the Southern Hemisphere. These rates assume that you are watching from rural areas away from all sources of light pollution. The actual activity one may see 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 evening activity this week.
The positions listed below are exact for Saturday night/Sunday morning December 14/15 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 which constellations are in 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. 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 06:32 (098) +23. This area of the sky is located in western Gemini, 3 degrees west of the 3rd magnitude star Mu Geminorum. Since this source is large and diffuse, any slow to medium speed meteor from eastern Taurus, northeastern Orion or western 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.
The Monocerotids
are currently active from a radiant located at 06:56 (104) +08. This area of the sky is located
in eastern Monoceros, 7 degrees west of the 3rd magnitude star Gomeisa (Beta
Canis Minoris). These meteors are
best seen near 0100 local standard time when the radiant lies highest above
the horizon. The peak for the Monocerotids occurred on December 8 when the
ZHR reached 3. Current rates should be 1-2 per hour. This shower would be
equally well seen from both hemispheres. At 42 km/sec. the Monocerotids produce
meteors of average velocity.
The Northern Apex source is now centered at 11:32 (173) +18. This position lies in eastern Leo, 3 degrees northwest of the 2nd magnitude Denebola (Beta Leonis). 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 western Coma Berenices, northwestern Virgo or eastern Leo 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 11:32 (173) -12. This position lies in a remote area of
northern Crater, 3 degrees southeast of the faint star Epsilon Crateris.
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,
central Hydra, Crater or southwestern 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 have now reached their plateau of top activity, which occurs during the entire last quarter of the year. One would currently expect to see perhaps 10 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 now rising from their annual low with perhaps 6 random meteors being seen per hour during the early morning hours and 2 per hour during the evening. Lunar interference reduces the evening activity this week.
Clear Skies!