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(meteorobs) Meteor Activity Outlook for Jan 16-22, 2004
The moon reaches its new phase on Wednesday January 21. At this time the
moon lies near the sun in the sky as seen from the Earth. It will rise and
set with the sun and will not interfere with observing. This weekend the
waning crescent moon will rise during the late morning hours and will not be
much of a problem at all. The estimated total hourly rates for evening
observers this week should be near two for those in the Northern Hemisphere
and three for those south of the equator. For morning observers the
estimated total hourly rates should be near twelve for those located in the
Northern Hemisphere and fifteen 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.
The radiant positions listed below are exact for Saturday night/Sunday
morning January 17/18. 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 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 08:44 (131) -48. This position lies in
western Vela some five degrees east 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 Antihelion radiant is now centered at 08:48 (132) +17. This area of the
sky is located in central Cancer, very close to the fourth magnitude star
Delta Cancri. Since this radiant is large and diffuse, any slow to medium
speed meteor from the entire constellation of 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 three shower members per hour from areas north of
the equator and one 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 Alpha Hydrids (AHY) is another shower listed among radiants of the Dutch
Meteor Society. The date of maximum activity was January 15 with a predicted
ZHR of two. Current rates would be most likely less than one shower member
per hour. With such low activity care must be taken to exclude any sporadic
activity from the Alpha Hydrid count. The radiant currently lies at 09:00
(135) -12. This position lies in western Hydra six degrees southwest of the
second magnitude star Alphard (Alpha Hydrae). This radiant is seen equally
well from both hemispheres. The area of the sky is also best placed near
0200 local standard time. At 44 km/sec. the Alpha Hydrids produce meteors of
average velocity.
The Alpha Crucids (ACR) is yet another shower listed among the radiants of
the Dutch Meteor Society. The date of maximum activity is January 16 with a
predicted ZHR of three. Like the previous weak showers, care must be taken
to exclude any sporadic activity from the Alpha Crucid count. The radiant
currently lies at 12:56 (194) -64. This position lies in southeastern Crux
some three degrees southeast of the first magnitude star Acrux (Alpha
Crucis). Due to the far southern declination this shower is not well seen
north of the northern equatorial regions. The area of the sky is also best
placed just before dawn when it lies highest in the sky. At 50 km/sec. the
Alpha Crucids produce meteors of medium swift velocity.
The Northern Apex radiant is now centered at 13:48 (207) +05. This position
lies in northern Virgo, six degrees northeast of the third magnitude star
Zeta 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 southwestern
Bootes could be a candidate from this source. Rates would be now close to
two per hour regardless of your location.
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 13:48 (207) -25. This position lies in easternmost Hydra some
four degrees northwest of the third magnitude star Pi Hydrae. 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 northern Centaurus, southwestern Libra, 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 Sporadic rates for the Northern Hemisphere are now past their annual
peak. One would currently expect to see perhaps seven 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 two
random meteors can be seen per hour from the Northern Hemisphere. Rates seen
from the Southern Hemisphere are now slightly stronger than those seen in
the northern skies with perhaps eight random meteors being seen per hour
during the early morning hours and three per hour during the evening.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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