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(meteorobs) Meteor Activity Outlook for Sep 5-11, 2003
The moon is full on Wednesday September 10 and will be located opposite the
sun in the sky. This weekend, the waxing gibbous moon will set early enough
to allow an hour or two of dark sky viewing before the onset of morning
twilight. 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 ten
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 September 6/7. 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 Antihelion radiant is now located at 23:56 (359) 00. This area of the
sky is located in western Pisces, seven degrees south of the fourth
magnitude star Omega Piscium. Any slow to medium speed meteor from the
northeastern Aquarius, northwestern Cetus 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 September Perseids (DAU) peak on the morning of September 9 with
predicted ZHR's of six. The radiant is currently located at 03:48 (057) +46,
which places it in central Perseus, one degree southeast of the third
magnitude star Delta Persei. This weekend I would expect rates of one to
two shower members per hour. 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 64km/sec., the average September Perseid is swift.
The Northern Apex radiant is now located at 04:56 (074) +38. This position
lies in western Auriga, one degree northwest of the fifth magnitude star
Omega Aurigae. 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 04:56 (074) +08. This position lies in western Orion, one
degree northeast 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) peaked on the morning of September 1 with very low
rates. The radiant is currently located at 06:04 (091) +42, which places it
in eastern Auriga, three degrees south of the second magnitude star
Menkalinan (Beta Aurigae). Like the September Perseids, 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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