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(meteorobs) Meteor Activity Outlook for Nov. 14-20, 2003
The moon reaches its last quarter phase on Monday November 17. At this time
the moon lies ninety degrees west of the sun and will rise near midnight
local standard time. This will cause some interference with morning
observing week with each morning getting more favorable as the moon wanes
and rises later in the night. The estimated total hourly rates for evening
observers this week should be near two for those in the Northern Hemisphere
and one in the Southern Hemisphere. For morning observers the estimated
total hourly rates should be near sixteen 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. Morning rates are reduced due to
moonlight.
The radiant positions listed below are exact for Saturday night/Sunday
morning November 15/16. 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 Delta Eridanids are listed among the radiants of the Dutch Meteor
Society. This shower peaked on November 13 with an estimated ZHR of only
one. The radiant is located at 03:52 (058) -01. This position lies in
northern Eridanis, twelve degrees north of the third magnitude star Zaurak
(Gamma Eridani). These meteors are best seen near 0000 (midnight) local
standard time when the radiant lies highest above the horizon. At 31 km/sec.
the Delta Eridanids produce meteors of average and slow velocities.
The Antihelion radiant is now centered at 04:36 (069) +22. This area of the
sky is located in central Taurus, five degrees northwest of the first
magnitude star Aldebaran (Alpha Tauri). Since this radiant is large and
diffuse, any slow to medium speed meteor from northeastern Orion or central
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. We are now seeing an increase in the antihelion activity
as the Earth encounters debris from comet 1P Encke in addition to the normal
material. At this time expect to see 3 shower members per hour from areas
north of the equator and 2 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 report to the IMO should list these meteors as Northern
Taurids (NTA) or Southern Taurids (STA) depending on whether the meteors
radiant from north or south of the ecliptic.
The Alpha Monocerotids reach maximum activity on November 22 with normally
low rates. This shower has the strange distinction of producing short but
very strong outbursts in years ending in "5". We are only two years away
from the next outburst so activity this year may be better than average. The
radiant is currently located at 07:24 (111) +01. This position lies in
southwestern Canis Minor, four degrees southwest of the zero magnitude star
Procyon (Alpha Canis Minoris). These meteors are best seen near 0300 local
standard time when the radiant lies highest above the horizon in a dark sky.
At 65 km/sec. the Alpha Monocerotids produce mostly swift meteors.
The Zeta Puppids are also listed among the radiants of the Dutch Meteor
Society. This shower peaked on November 13 with an estimated ZHR of only
three. The radiant is located at 07:56 (119) -43. This position lies in
southeastern Puppis, four degrees southwest of the second magnitude star
Zeta Puppis. These meteors are best seen near 0400 local standard time when
the radiant lies highest above the horizon in a dark sky. At 41 km/sec. the
Zeta Puppids produce meteors of average velocity.
The Northern Apex radiant is now centered at 09:36 (144) +29. This position
lies in northwestern Leo, three degrees northwest of the fourth magnitude
star Mu Leonis.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 northeastern Cancer,
northwestern Leo or southwestern Leo Minor could be a candidate from this
source. This source should provide at least two meteors per hour for those
in the Northern Hemisphere and less than one per hour for those in the
Southern Hemisphere. Be careful when determining shower association as the
Leonid radiant lies close by. Both radiants product swift, often trained
meteors.
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 09:36 (144) -01. This position lies in western Hydra some
eight degrees northeast of the second magnitude star Alphard (Alpha 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 western Hydra, southwestern Leo or
western Sextans could be a candidate from this source. Rates would be now
close to two per hour regardless of your location.
The Leonids have several peaks occurring throughout this period. Rather than
list all the predicted peaks, I would encourage everyone to view the morning
sky for Leonid activity as much as possible this week. The Earth crosses the
center of the orbit of comet Temple-Tuttle on November 18. On this date the
radiant is located at 10:12 (153) +22. This position lies in northwestern
Leo, two degrees northwest of the second magnitude star Algeiba (Gamma
Leonis). The radiant lies highest above the horizon in a dark sky just
before the start of morning twilight. At 71 km/sec. the Leonids produce
mostly swift meteors with a high percentage of persistent trains.
The Sporadic rates for the Northern Hemisphere are now near 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 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
four random meteors being seen per hour during the late morning hours and
two during the evening hours. Morning rates are reduced due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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