(meteorobs) Meteor Activity Outlook for September 24-30, 2004

[Robert Lunsford]

This upcoming period will see the moon passing its full phase on September
28. This weekend the waxing gibbous moon will set during the early morning
hours allowing a brief period of dark skies between moonset and the start 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
for those observers south of the equator. Meteor rates are lower than usual
due to moonlight. For morning observers the estimated total hourly rates
should be near ten for those located in the Northern Hemisphere and six 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 25/26. 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 planetariums) 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 latitude. 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 further down the list rise later in
the night.

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. Current rates would be near less than one shower member per hour.
Those viewing from near the equator are best situated for viewing this
shower. The radiant is located in western Pisces at 23:00 (345) -02. This
position is six degrees south of the faint star Beta Piscium. 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 01:12 (018) +07. This area of the
sky is located in southern Pisces, one degree southeast of the faint star
Zeta Piscium. Since this radiant is large and diffuse, any slow to medium
speed meteor from  southern Pisces, southwestern Aries or northern 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 one shower member 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 Delta Aurigids (DAU) reached a secondary peak on September 23 with an
expected ZHR of 3. Current rates are expected to be near one shower member
per hour. The radiant is currently located at 05:12 (078) +49, which places
it in northwestern Auriga, four degrees north of the brilliant first
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 near 05:00 local daylight time, when
it lies highest in the sky. At 64km/sec., the average Delta Aurigid is
swift. This shower is also known as the Epsilon Perseids and the September
Perseids.

The Northern Apex radiant is now centered at 06:12 (093) +38. This position
lies in eastern Auriga, three degrees northeast of the third magnitude star
Theta 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 northwestern Gemini,
northeastern Taurus or 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
Delta Aurigids as this radiant lies close to the western boundary 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 006:12 (093) +08. This position lies in eastern Orion, three
degrees east of the first magnitude variable star Betelgeuse (Alpha
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, western Monoceros
or southwestern Gemini 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 four 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
one random meteor 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 three random meteors being seen during the late morning hours
and one per hour during the evening. Rates are lower than usual due to
moonlight.

  SHOWER  MAXIMUM  POSITION  VELOCITY  CULMINATION

Kappa Aquarids Sep 18  23:00 (345) -02      19                   00:00
Antihelion (SPI)     ---     01:12 (018) +07      30                   02:00
Delta Aurigids    Sep 23  05:12 (078) +49      64                   05:00
Northern Apex      ---     06:12 (093) +38      65                   06:00
Southern Apex      ---     06:12 (093) +08      65                   06:00

Clear Skies!
Robert Lunsford
American Meteor Society