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(meteorobs) Meteor Activity Outlook for Dec. 12-18, 2003
The moon reaches its last quarter phase on Tuesday December 16. At this time
the moon lies ninety degrees west of the sun and will rise near local
midnight. During this entire period bright moonlight will reduce the meteor
activity seen during the normally productive morning hours. The estimated
total hourly rates for evening observers this week should be near two for
those in the Northern Hemisphere and one in the Southern Hemisphere. For
morning observers the estimated total hourly rates should be near sixteen
for those located in the Northern Hemisphere and eight 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.
Rates are reduced during the morning hours due to moonlight.
The radiant positions listed below are exact for Saturday night/Sunday
morning December 13/14. The radiants do not change greatly day to day so the
given 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 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 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 radiant is now centered at 06:28 (097) +23. This area of the
sky is located in western Gemini, three degrees southwest of the third
magnitude star Epsilon Geminorum. Since this radiant is large and diffuse,
any slow to medium speed meteor from western Gemini, northeastern Orion,
southern Auriga or eastern Taurus could be a candidate for this shower. The
center of this area 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 2
shower members per hour from areas north of the equator and 1 per hour for
locations south of the equator. Don't confuse these meteors with the more
numerous Geminid meteors. The Geminid radiant lies approximately twenty
degrees to the northeast and will be much more active, especially this
weekend. Unless one is viewing directly between these two radiants, it would
be difficult to separate these two sources unless the meteors are moving due
north or south from their respective radiants.
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
material 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 send their data to the International Meteor Organization
should call these meteors Chi Orionids (XOR).
The Monocerotids (MON) are not to be confused with the Alpha Monocerotids of
mid-November. This shower reached maximum activity (ZHR three) on December
9. The radiant is currently located at 06:52 (103) +08. This position lies
in northwestern Monoceros some five degrees southeast of the third magnitude
star Xi Geminorum, These meteors are best seen near 0200 local standard time
when the radiant lies highest above the horizon in a dark sky. At 42 km/sec.
the Monocerotids produce meteors of average velocity.
The Geminids (GEM) reach maximum activity on Sunday morning near 1200
Universal Time (7 am EST and 4 am PST). Moonlight from a waning gibbous moon
in the constellation of Leo will limit the number of Geminids seen this
year. Under these conditions peak rates would be reduced by at least fifty
percent meaning that one can expect to see no more than 30-40 Geminids per
hour when the radiant lies high in the sky. The radiant is currently located
at 07:28 (112) +33. This position lies in northeastern Gemini only one
degree northwest of the second magnitude star Castor (Alpha Geminorum).
These meteors are best seen near 0200 local standard time when the radiant
lies highest above the horizon. At 42 km/sec. the Geminids produce meteors
of average velocity. Good Geminid activity should also be visible on
December 15 (evening of the fourteenth in the US) with the moon slightly
less of a problem.
The Puppid/Velids (PUP) are most likely a continuation of the November Zeta
Puppid activity listed by the Dutch Meteor Society. This shower peaked near
December 7 with an estimated ZHR of ten. There are several suspected
radiants in this area combining to produce this activity. The main radiant
is located at 08:32 (128) -45. This position lies in western Vela, five
degrees northeast of the second magnitude star Gamma Velorum. These meteors
are best seen near 0400 local standard time when the radiant lies highest
above the horizon. Due to the far southern declination these meteors are
only visible from areas southward of latitude forty-five degrees north. At
41 km/sec. the Zeta Puppids produce meteors of average velocity.
The Sigma Hydrids (HYD) reach maximum activity on December 12 with an
estimated ZHR (zenith hourly rate) of two. The radiant is currently located
at 08:36 (129) +01. This position lies in western Hydra only two degrees
southwest of the fourth magnitude star Sigma Hydrae. These meteors are best
seen near 0400 local standard time when the radiant lies highest above the
horizon. At 58 km/sec. the Sigma Hydrids produce mostly swift meteors.
The Northern Apex radiant is now centered at 11:28 (172) +18. This position
lies in eastern Leo, three degrees southeast of the third magnitude star
Zosma (Delta Leonis). This area of the sky is best placed for viewing during
the last dark hour before dawn when it lies highest in the sky. Since this
radiant is large and diffuse, any meteor from eastern Leo or western Coma
Berenices could be a candidate from this source. This source should provide
at least two meteors per hour for those in the Northern Hemisphere and one
per hour for those in the Southern Hemisphere. Those who send their data to
the International Meteor Organization should call these meteors Coma
Berenicids (COM).
Like the antihelion area, 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. This is
not really a "shower" per se, but an artificial radiant created by the
Earth's motion through space. Meteors from both branches are normally
included in the sporadic count. I feel it is a worthy project to see if it
is possible to distinguish these meteors from the normal sporadic
background. On rare occasions there are meteors with a zero inclination that
radiate precisely from the apex point on the ecliptic, exactly 90 degrees
west of the sun. In simplistic terms, these meteors are seldom seen since
the Earth "sweeps clean" much of the material that shares the same orbit as
our planet. Much more material 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.
The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 11:28 (172) -12. This position lies in central Crater very
close to the faint star Kappa Crateris. Like the northern apex, these
meteors are best seen toward dawn when the radiant lies highest above the
horizon in a dark sky. Since this radiant is also large and diffuse, any
meteor from the entire constellation of Crater could be a candidate from
this source. Rates would be now close to one per hour regardless of your
location.
The Sporadic rates for the Northern Hemisphere are now near their annual
peak. One would expect to see perhaps four random meteors per hour during
the last hours before dawn from rural observing sites. This estimate and the
estimate for the Southern Hemisphere do not include meteors from the apex
radiants. During the evening hours perhaps three random meteors can be seen
per hour. Rates seen from the Southern Hemisphere would be approximately
three random meteors being seen per hour during the late morning hours and
one during the evening hours. Morning rates are reduced in both hemispheres
due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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