(meteorobs) Meteor Activity Outlook for September 10-16, 2004

[Robert Lunsford]

This upcoming period will see the moon passing its new phase on September 14
and then entering the evening sky. With the moon close to the sun during
this entire period, this will be the best time this month to view meteor
activity. The estimated total hourly rates for evening observers this week
should be near four for those in the Northern Hemisphere and two for those
observers south of the equator. For morning observers the estimated total
hourly rates should be near twenty four 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 September 11/12. These positions do not change greatly day to day so
the listed coordinates 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.

These are the showers that may be observed this week:

The Kappa Aquarids (KAQ) are listed among the radiants of the Dutch Meteor
Society. At peak activity (September 18) this radiant only produces a ZHR of
three. Being a week before the peak, current rates would be near one. The
radiant is located in central Aquarius at 22:12 (333) -07. This position is
one degree northwest of the 4th magnitude star Theta Aquarii. The radiant is
best placed for viewing near midnight local daylight time, when the radiant
lies highest in the sky. At 19km/sec., the average Kappa Aquarid is easily
recognized by its very slow velocity.

The Anthelion radiant is now centered at 00:16 (004) +02. This area of the
sky is located in western Pisces, six degrees southeast of the fourth
magnitude star Omega Piscium. Since this radiant is large and diffuse, any
slow to medium speed meteor from eastern Aquarius, southern Pegasus, western
Pisces or northwestern Cetus 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
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. There
is also the possibility that some of this activity may be caused by the
"Jupiter family of comets", comets which have been altered by Jupiter's
gravity into much shorter orbits. 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 anthelions 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. IMO observers should label these meteors as
"Piscids" (SPI).

The Alpha Triangulids (ATR) may produce notable activity this year.
According to comet and meteor researcher Gary W. Kronk, this shower seems to
have a period of 5 or 6 years. The last period of good activity was recorded
in 1998 and 1999. The other known years, when two or more experienced meteor
observers saw good activity visually, were in 1934, 1940, 1951 and 1993. So,
it is possible that enhanced activity might be seen this year. The radiant
is currently located at  02:00 (030) +29, which places it in southern
Triangulum, two degrees southeast of the third magnitude star Alpha
Trianguli . The radiant is best placed near 0300 local daylight time, when
it lies highest above the horizon. I would estimate the velocity near
45km/sec., which is slightly above average. There is also a possible
sub-radiant located five degrees further south near the second magnitude
star Hamal (Alpha Arietis). Your observations of this activity is very
important, especially this year when the moon is also out of the way.

The September Perseids (DAU) peaked on the morning of September 8 with an
expected ZHR of 6. The radiant is currently located at  04:08 (062) +47,
which places it in eastern Perseus, two degrees southwest of the fourth
magnitude star Mu Persei . 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. This
shower is also known as the Epsilon Perseids and the Delta Aurigids. Those
who report to the IMO should label these meteors as "DAU".

The Northern Apex radiant is now centered at 05:16 (079) +38. This position
lies in western Auriga, very close to the faint star Mu Auriga. 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 eastern Perseus, northern Taurus or western Auriga could be
a candidate from this source. Rates would be now close to three per hour for
observers north of the equator and less than one per hour for those
observers south of the equator. Observers who view far from this radiant
must be careful not to list these meteors as September Perseids or Alpha
Aurigids as both radiants lie within the boundaries of the Northern Apex
radiant.

Like the anthelion area, both apex areas are active all year long and travel
approximately one degree eastward per day. Unlike the anthelion 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 05:16 (079) +08. This position lies in western Orion, three
degrees northwest of the second magnitude star Bellatrix (Gamma Orionis).
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 Orion, northeastern Eridanus or
southeastern Taurus could be a candidate from this source. Rates would now
be near two per hour regardless of your location.

The Sporadic rates for the Northern Hemisphere are now increasing toward
their last quarter plateau. One would expect to see perhaps twelve random
meteors per hour during the last hours before dawn from rural observing
sites. This estimate and the morning estimate for the Southern Hemisphere do
not include the apex meteors listed above. During the evening hours perhaps
four random meteors can be seen per hour from the Northern Hemisphere. Rates
seen from the Southern Hemisphere are now lower than those seen in the north
with perhaps eight random meteors being seen during the late morning hours
and two per hour during the evening.

One other source of activity during this period may be the "September
Taurids".  This radiant has not been pinpointed yet but most reports have it
lying somewhere between the Hyades and Pleiades star clusters in western
Taurus. Meteors from this radiant would be best seen just before dawn, when
it lies highest in the sky. Meteors from this radiant should have a velocity
near 60km/sec., which is swift. Remember that meteors seen near the radiant
would appear to travel slower than those seen further away.

Clear Skies!
Robert Lunsford and George Gliba
American Meteor Society