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(meteorobs) Meteor Activity Outlook for Jan 2-8, 2004
The moon reaches its full phase on Wednesday January 7. At this time the
moon lies opposite the sun in the sky and will be in the sky all night long.
This weekend the moon will set several hours before the start of morning
twilight allowing a brief window of opportunity to view under dark skies.
The estimated total hourly rates for evening observers this week should be
near one for everyone no matter your location. For morning observers the
estimated total hourly rates should be near twenty for those located in the
Northern Hemisphere and twelve 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. Evening rates are reduced due
to moonlight.
The radiant positions listed below are exact for Saturday night/Sunday
morning January 3/4. 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 07:52 (118) +21. This area of the
sky is located in eastern Gemini, seven degrees south of the first magnitude
star Pollux (Beta Geminorum). Since this radiant is large and diffuse, any
slow to medium speed meteor from eastern Gemini or Cancer 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 3 shower members per hour from areas north of the
equator and 1 per hour for locations 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
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 Delta Cancrids (DCA).
The Gamma Velids (GVE) are the first of many weak southern showers active
during January and February. The Gamma Velids are listed among the radiants
of the Dutch Meteor Society and reach maximum activity on January 6. Current
rates would be low, most likely less than one shower member per hour. The
radiant is currently located near 08:16 (124) -47. This position lies in
western Vela, only one degree northeast of the second magnitude star Gamma
Velorum. The radiant lies highest in the sky between 0100 and 0200. This
shower is not visible north of latitude 45 north. At 35 km/sec. the Gamma
Velids produce meteors of average velocity.
The Northern Apex radiant is now centered at 12:52 (193) +10. This position
lies in northern Virgo, two degrees southwest of the third magnitude star
Vindemiatrix (Epsilon Virginis). 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 northern Virgo
or southern Coma Berenices could be a candidate from this source. Rates
would be now close to two per hour regardless of your location. 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 12:52 (193) -20. This position lies on the Corvus/Virgo
border some twelve degrees southwest of the first magnitude star Spica
(Alpha Virginis). 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 Corvus, eastern
Hydra or southern Virgo could be a candidate from this source. Rates would
be now close to one per hour in the Northern Hemisphere and two per hour in
the Southern Hemisphere.
The Quadrantids (QUA) reach maximum activity on January 4 near 0600
Universal Time. This corresponds to 0100 (1am) EST and 2200 (10pm on January
3) PST. Western Europe, northwestern Africa and the north Atlantic area are
the prime longitudes in which to view this shower. The radiant is located at
15:20 (230) +49. This position lies in a sparse area of northern Bootes, ten
degrees south of the third magnitude star Iota Draconis. Rates can exceed
one hundred shower members per hour but with the moon spoiling the display
for most areas, I would expect most observers to see rates near 25 per hour
at best. At 41 km/sec. the Quadrantids produce meteors of average velocity
with few persistent trains.
The Sporadic rates for the Northern Hemisphere are now just past their
annual peak. One would expect to see perhaps six 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 one random meteor can be
seen per hour. Sporadic rates seen from the Southern Hemisphere are
increasing toward a peak this month. One would see approximately six random
meteors per hour during the late morning hours and one per hour during the
evening. Evening rates are reduced due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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