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(meteorobs) Meteor Activity Outlook for Aug 28-Sep 4, 2003
The moon reaches its first quarter phase on Wednesday September 3. At this
time the moon will lie ninety degrees west of the sun and will set near
0100. Therefore the moon will set as the stronger morning activity begins
and will not cause any interference to morning observers this week. 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
eighteen 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.
Evening rates are reduced due to moonlight.
The radiant positions listed below are exact for Saturday night/Sunday
morning Aug 30/31. The positions do not change greatly day to day so they
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 North Iota Aquarids (NIA) are near the end of their activity for 2003.
The radiant is currently located at 22:32 (338) -05. This area of the sky is
located in northern Aquarius, one degree west of the fifth magnitude star
Kappa Aquarii. This radiant is most active near 0100 LDT when it lies
highest in the sky. Maximum activity occurred on August 20 with a ZHR of
three. Current rates would be less than one per hour. At 31 km/sec. the
NIA's are a bit slower than your average meteor.
The Antihelion radiant is now located at 23:28 (352) -03. This area of the
sky is located in southwestern Pisces, four degrees south of the fifth
magnitude star Kappa Piscium. Any slow to medium speed meteor from the
northeastern Aquarius or western Pisces could be a candidate for this
shower. The radiant is best placed near 0200 local daylight time when it
lies on the meridian and is highest in the sky. At this time expect to see
two shower members per hour no matter your location.
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 Piscids
(SPI)
The Pi Eridanids (ERI) are minor shower listed among the radiants of the
Dutch Meteor Society. The peak activity is listed as August 27 with a ZHR of
four. The current radiant position lies at 03:40 (055) -14, which places it
in western Eridanus, two degrees southwest of the fourth magnitude star Pi
Eridani. The radiant is best placed just before the start of morning
twilight, when it lies highest above the horizon in a dark sky. At
59km/sec., a majority of these meteors will move swiftly. Brighter shower
members should produce trains
The Gamma Doradids (GDO) are another obscure minor shower listed among the
radiants of the Dutch Meteor Society. The peak activity is listed as August
30 with a ZHR of five. The current radiant position lies at 04:04 (061) -50,
which places it in eastern Horologium some four degrees northwest of the 3rd
magnitude star Gamma Dorado. Due to the extreme southern declination, this
shower is only visible from the northern tropics southward. The radiant is
best placed just before the start of morning twilight. At 41km/sec., these
meteors are of average velocity.
The Northern Apex radiant is now located at 04:28 (067) +37. This position
lies in eastern Perseus, five degrees southeast of the third magnitude star
Epsilon Persei. 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
southwestern Auriga, eastern Perseus or northern Taurus could be a good
candidate for this shower. This source should provide at least three meteors
per hour for those in the Northern Hemisphere and less than 1 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 04:28 (067) +07. This position lies in southern Taurus, four
degrees west of the third magnitude star Pi 3 Orionis. 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 northeastern Eridanus,
northwestern Orion or southern Taurus could be a candidate from this source.
Rates would be now close to two per hour regardless of your location.
The Alpha Aurigids (AUR) peak on the morning of September 1 with an average
ZHR of seven. The radiant is currently located at 05:32 (083) +42, which
places it in central Auriga, four degrees southeast of the zero magnitude
star Capella (Alpha Aurigae). Due to the extreme northern declination, this
shower is only visible from the southern tropics northward. The radiant is
best placed just before the start of morning twilight, when it lies highest
in the sky. At 66km/sec., the average Alpha Aurigid is swift.
The Sporadic rates for the Northern Hemisphere are now rising slowly toward
their peak, which occurs during the last quarter of the year. 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 two 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 one during the
evening hours. Evening rates are reduced due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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