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(meteorobs) Meteor Activity Outlook for Oct. 24-30, 2003
The moon reaches its new phase on Saturday October 25. At this time the moon
lies in the vicinity of the sun as seen from the Earth. It will rise and set
with the sun and not be visible in the night sky. Later in the period the
waxing crescent moon will enter the evening sky yet will set well before
midnight. The estimated total hourly rates for evening observers this week
should be near three for those in the Northern Hemisphere and two in the
Southern Hemisphere. For morning observers the estimated total hourly rates
should be near twenty 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 October 25/26. 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 03:12 (048) +17. This area of the
sky is located in eastern Aries, two degrees south of the fourth magnitude
star Delta Arietis. Since this radiant is large and diffuse, any slow to
medium speed meteor from eastern Aries or western 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 three shower members per hour from locations
north of the equator and two shower members per hour from 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 report to the IMO should list these meteors as Northern
Taurids (NTA) or Southern Taurids (STA).
The Orionids (ORI) peaked on Tuesday morning October 21 with predicted ZHR's
of twenty. The radiant is currently located at 06:36 (099) +16, which places
it in southwestern Gemini, very close to the second magnitude star Alhena
(Gamma Geminorum). The radiant is best placed near 0300 local standard time,
when it lies on the meridian and highest in the sky. Current rates should be
near 5 shower members per hour. At 66km/sec., the average Orionid is swift.
What makes this shower interesting is the fact it is produced by the debris
from Halley's Comet, now seventeen years past its last trip to the inner
solar system. Despite this fact the shower is not affected by the position
of the comet and produces fairly stable rates year after year.
The Epsilon Geminids (EGE) peaked on October 18 with predicted ZHR's of two.
This radiant is currently located at 07:20 (110) +27, which places it in
central Gemini, five degrees southwest of the first magnitude star Pollux
(Beta Geminorum). This weekend I would expect very week rates of less than
one shower member per hour. The radiant is best placed near 0400 LST when it
lies highest in the sky. At 70km/sec., the average Epsilon Geminid is swift
with a high percentage of persistent trains.
The Northern Apex radiant is now centered at 08:12 (123) +34. This position
lies in southern Lynx, eight degrees northeast of the first magnitude star
Pollux (Beta Geminorum).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 northwestern Gemini,
northwestern Cancer or southern Lynx could be a candidate from this source.
This source should provide at least three meteors per hour for those in the
Northern Hemisphere and less than one per hour for those in the Southern
Hemisphere.
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 08:12 (123) +04. This position lies on the Canis Minor/Hydra
border some six degrees southeast of the zero magnitude star Procyon (Alpha
Canis Minoris). 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 northwestern Hydra,
southwestern Cancer, southeastern Gemini or Canis Minor could be a candidate
from this source. Rates would be now close to two 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 eight random meteors per hour during
the last hours before dawn from rural observing sites. This estimate and the
estimate for the Southern Hemisphere does 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 six
random meteors being seen per hour during the late morning hours and two
during the evening hours.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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