(meteorobs) Meteor Activity Outlook for September 3-9, 2004

[Robert Lunsford]

This upcoming period will see the moon rising later at night and finally
being limited to the morning sky. Since the moon will be near its last
quarter phase this weekend, it will still cause considerable interference to
sky watchers. The good news though is that the glare is much less than that
of the full moon and successful meteor observations can be undertaken if one
keeps the moon out of their field of view. Under transparent skies in rural
regions, the Milky Way can be seen within thirty degrees of the moon. The
estimated total hourly rates for evening observers this week should be near
three 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 twelve for those located in the Northern Hemisphere and eight
for those in the Southern Hemisphere. Morning rates are reduced due to
moonlight. 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 4/5. 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 two weeks before the peak, current rates would be very low. The
radiant is located in northeastern Capricornus at 21:44 (326) -10. This
position is six degrees north of the 3rd magnitude star Nashira (Delta
Capricorni). 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 23:48 (357) -01. This area of the
sky is located in western Pisces, three degrees southeast of the faint star
Lambda 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 September Perseids (DAU) peak on the morning of September 8 with an
average ZHR of 6. The radiant is located at  03:40 (055) +46, which places
it in central Perseus, only 2 degrees south of the 3rd magnitude star Delta
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 04:48 (072) +37. This position
lies in southeastern Peresus, six degrees southwest of the third magnitude
star Eta Aurigae. 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 two 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 04:48 (072) +07. This position lies in western Orion, very
close to the third magnitude star known as 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. Since this radiant is also large and
diffuse, any meteor from western Orion, northwestern Eridanus or southern
Taurus could be a candidate from this source. Rates would now be near one
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 five 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
three 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 four random meteors being seen during the late morning
hours and two per hour during the evening. Morning rates are reduced due to
moonlight.

Toward the end of this period some activity may be noticed from the
"September Taurids" and the "Aries-Triangulid" radiants. Rates are expected
to be low during this period but some activity may be seen if one faces
toward these radiants. The September Taurids have a radiant lying somewhere
between the Hyades and Pleiades star clusters in western Taurus. The
Aries-Triangulids appear to have two radiants, the main one lying near Alpha
Trianguli and a secondary radiant lying near the bright star Hamal (Alpha
Arietis). The meteors from these radiants would usually be medium-swift. A
more detailed description of these showers will be included in next week's
outlook.

Clear Skies!
Robert Lunsford
AMS Operations Manager