[Prev][Next][Index][Thread]

(meteorobs) Meteor Activity Outlook for December 21-27, 2001



The moon reaches its first quarter phase on Saturday December 22. At
this time it will set near midnight local time allowing a good view of
the morning skies. The moon will become troublesome toward the end of
the period as it approaches full and will be in the sky most of the
night. The estimated total hourly rates for evening observers this week
should be near 1 for everyone regardless of location. For morning
observers the estimated total hourly rates should be near 13 for the
Northern Hemisphere and 9 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. Evening rates are
reduced by moonlight during this period.

The positions listed below are exact for Saturday night/Sunday morning
December 22/23. 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 07:04 (106) +22. This area of
the sky is located in central Gemini 3 degrees west of the 3rd magnitude
star Delta Geminorum. Any slow to medium speed meteor from Gemini 
could be a good 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 see 1 per hour. 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. 

The Northern Apex radiant is now located at 12:04 (181) +15. This
position lies in southwestern Coma Berenices 4 degrees east of the 2nd
magnitude star Denebola (Beta Leonis). 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 eastern Leo, southwestern Coma
Berenices or northwestern Virgo could be a good candidate for this
shower. As seen from the Northern Hemisphere this source should produce
2 meteors per hour during the last few hours before dawn. Rates seen
from the Southern Hemisphere would be less at 1 per hour due to the
lower radiant altitude seen south of the equator. 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 12:04 (181) -15. This position lies in western Corvus, 3
degrees northwest of the 3rd magnitude star Gamma 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 western
Corvus or easter Crater 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 Ursids reach maximum activity on Saturday December 22. The radiant
position will then be located at 14:28 (217) +76 which places it in Ursa
Minor near the bright star Kochab (Beta Ursae Minoris). Peak rates are 
unpredictable. Video cameras caught a small outburst last year. Visual
rates were unimpressive. I would expect an observer with dark rural
skies to see up to 15 Ursids an hour. These meteors are usually faint
and difficult to see from urban locations. These are medium speed
meteors that are best seen just before dawn when the radiant lies
highest in the sky. Since the Ursids possess a average velocity
persistent trains are uncommon. Ursid meteors can be seen in any portion
of the sky but I would suggest facing toward the north to see the most 
Ursid activity. It is suggested that you have the radiant within your
field of view to help you associate Ursids from other meteors. You need
not stare directly at the radiant but just be sure that you can easily
see the bowl of the Little Dipper. Due to its high declination
(celestial latitude) these meteors are not visible from the Southern 
Hemisphere.

The Sporadic rates for the Northern Hemisphere are now near 7 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 1 random meteor can be seen per hour from the Northern
Hemisphere. Rates seen from the Southern Hemisphere are now  past their
annual low with perhaps 5 random meteors being seen per hour during the
late morning hours and 1 per hour during the evening.

Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
The archive and Web site for our list is at http://www.meteorobs.org
If you are interested in complete links on the 2001 LEONIDS, see:
http://www.meteorobs.org/storms.html
To stop getting email from the 'meteorobs' list, use the Web form at:
http://www.meteorobs.org/subscribe.html