(meteorobs) Meteor Activity Outlook for September 17-23, 2004

Robert Lunsford lunro.imo.usa at cox.net
Thu Sep 16 13:55:02 EDT 2004


With this edition I introduce a quick reference table that will list all the
radiants and important information, all in one easy location (at the end of
the outlook). Many thanks to Richard Kramer, who suggested an alternative
way to display this data. This upcoming period will see the moon passing its
first quarter phase on September 21. This weekend the waxing crescent moon
will set during the late evening hours allowing plenty of dark skies the
second half of the night. 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. Evening rates are lower
than usual due to moonlight. 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.

The radiant positions listed below are exact for Saturday night/Sunday
morning September 18/19. 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.  Current rates would be near 1-2 shower members per hour, depending
on your latitude. Those viewing from near the equator are best situated for
viewing this shower. The radiant is located in northern Aquarius at 22:36
(339) -05. This position is very close to the faint star Kappa 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 00:44 (011) +05. This area of the
sky is located in southern Pisces, four degrees south of the fourth
magnitude star Delta Piscium. Since this radiant is large and diffuse, any
slow to medium speed meteor from northeastern Aquarius, southeastern
Pegasus, southern 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 Delta Aurigids (DAU) reach a secondary peak on September 23 with an
expected ZHR of 3. The radiant is currently located at 04:40 (070) +48,
which places it in northeastern Perseus, six degrees northwest 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 05:44 (086) +38. This position
lies in central Auriga, three degrees west 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
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 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 05:44 (086) +08. This position lies in northern Orion, two
degrees west 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 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 eight 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
two 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 six random meteors being seen during the late morning hours and
one per hour during the evening.  Evening rates are lower than usual due to
moonlight.

SHOWER     MAXIMUM     POSITION     VELOCITY     CULMINATION*

Kappa
Aquarids           Sep  18        22:36 (339) -05     19 Km/Sec     00:00
(KAQ)

Antihelion            ---             00:44 (011) +05     30 Km/Sec    02:00
(SPI)

Delta Aurigids   Sep  23        04:40 (070) +48     64 Km/Sec     05:00
(DAU)

Northern Apex    ---             05:44 (086) +38     65 Km/Sec     06:00

Southern Apex    ---             05:44 (086) +08     65 Km/Sec     06:00

*Expressed in Local Daylight Time

Clear Skies!
Robert Lunsford
American Meteor Society



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