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(meteorobs) Meteor Activity Outlook for January 4-10, 2002
The moon reaches its last quarter phase on Saturday January 6. At this
time it will rise near midnight local time. With each passing night the
moon will rise later, allowing a better look at the more active morning
sky. The estimated total hourly rates for evening observers this week
should be near 2 for everyone regardless of location. For morning
observers the estimated total hourly rates should be near 9 for the
Northern Hemisphere and 12 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 rates will also depend on factors
such as personal light and motion perception, local weather conditions,
alertness and experience in watching meteor activity. Morning rates are
reduced by moonlight during this period.
The positions listed below are exact for Saturday night/Sunday morning
January 6/7. The positions do not change greatly day to day so they may
be used during this entire period. Most star atlas's (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 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 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 would
be seen 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 located at 08:04 (121) +20. This area of
the sky is located in western Cancer some 8 degrees west of the naked
eye open star cluster M44, also known as the beehive or Praesepe. Any
slow to medium speed meteor from western Cancer or eastern Gemini could
be a candidate for this shower. This 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 at least 2 shower members per hour
from locations in the Northern Hemisphere. Observers south of the
equator will most likely be limited to 1 per hour or less, owing to the
lower radiant altitude. Unlike most of the annual showers the antihelion
radiant is produced by debris from unknown sources orbiting in a direct
motion like the earth. These sources are most likely asteroids, which
produce stony and metallic debris whose density is much greater that
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 radiant is active all
year from an area of the sky nearly opposite that of the sun. The
radiant will travel approximately one degree eastward per day and
travels through many different constellations over the course of a year.
It is easiest to simply list these meteors as "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 reports with the I.M.O.
should label these meteors as Delta Cancrids (DCA).
The Gamma Velids are listed among the radiants of the Dutch Meteor
Society. Maximum activity is predicted for January 5 with a zenith
hourly rate of only 2. The radiant is located at 08:24 (126) -47 which
places it in western Vela 2 degrees northeast of the 2nd magnitude star
Gamma Velorum. This area of the sky is best placed near 0100 local
time. I would not expect any of this activity to be seen from the
Northern Hemisphere and rates of only 1-2 per night from far southern
observing sites. The Gamma Velids are of medium velocity when seen high
in the sky, far from the radiant. Care must be taken with this shower
and all weak showers as the chances of sporadics lining up with the
radiant are as great as the possibility of actual shower members
being produced.
The Alpha Hydrids is another obscure winter shower listed among the
radiants of the D.M.S. Maximum activity is reported to occur on January
14 with a maximum zenith hourly rate of 2. The current radiant is
located at 08:32 (128) -11. This area of the sky is located in
southwestern Hydra some 13 degrees southwest of the bright orange star
Alphard (Alpha Hydrae). It reaches the meridian near 0100. At this time
it is located highest in the sky and best placed for viewing. Any shower
members would also have medium velocities.
The Alpha Crucids is another obscure southern radiant producing little
activity. Australian observers report a maximum zenith hourly rate of 3.
Maximum activity occurs on January 15 so visual rates this week would
most likely be less than 1 per hour. The Alpha Crucid radiant is located
at 12:12 (183) -60. This area of the sky is located in central Crux just
west of the 4th magnitude star Epsilon Crucis. This area of the sky is
not visible north of 30 degrees north latitude and is best seen from far
southern locations just before dawn. These meteors are of medium
velocity comparable to the better known Lyrids of April.
The Northern Apex radiant is now located at 13:04 (196) +09. This
position lies in northwestern Virgo 2 degrees southeast of 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 radiant is diffuse any meteors from northwestern Virgo,
southeastern Coma Berenices or southwestern Bootes could be a good
candidate for this shower. This source should provide 1-2 meteors per
hour during the last few hours before dawn regardless of your location.
Those who send reports to the I.M.O. should label these meteors as Coma
Berenicids (COM).
Like the antihelion radiant both apex radiants 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 should
also be noted in some manner as to which branch of the apex complex they
appear to radiate.
The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 13:04 (196) -21. This position lies in extreme southern
Virgo 3 degrees northwest of the 3rd magnitude star Gamma Hydrae. 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
southern Virgo or eastern Hydra could be a candidate from this source.
Rates would be close to 2 per hour from the Southern Hemisphere and 1
per hour from the Northern Hemisphere.
The Sporadic rates for the Northern Hemisphere are now in decline and
will do so until June. One would expect to see perhaps 4-5 random
meteors per hour during the last hours before dawn from rural observing
sites. During the evening hours perhaps 2-3 random meteors can be seen
per hour. Rates seen from the Southern Hemisphere would now be a bit
better than those seen in the Northern Hemisphere with perhaps 5-6
random meteors being seen per hour during the late morning hours and 2-3
during the evening hours. Morning rates are reduced due to moonlight.
Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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