(meteorobs) Meteor Activity Outlook for October 15-21, 2004

[Robert Lunsford]

This upcoming period will see the moon passing its first quarter phase on
Wednesday October 20. This weekend the waxing crescent moon will set during
the early evening hours and will not cause any interference to meteor
observers. 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. For morning observers the estimated total
hourly rates should be near twenty four 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 October 16/17. 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 Anthelion radiant is now centered at 02:36 (039) +15. This area of the
sky is located in central Aries, eight degrees southeast of the second
magnitude star Hamal (Alpha Arietis). Since this radiant is large and
diffuse, any slow to medium speed meteor from eastern Pisces, central Aries,
northeastern Cetus or western Taurus could be a candidate for this shower.
The center of this area is best placed near 0100 local daylight time when it
lies on the meridian and is highest in the sky. At this time expect to see
three shower members per hour from the Northern Hemisphere and two per hour
south of the equator.

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 either
"Northern or Southern Taurids" (NTA or STA), depending on if the radiant
seems to be north or south of the ecliptic.

 The Delta Aurigids (DAU) have produced unusual activity this week. Normally
rates this time of year are very low but in recent days rates near five
shower members per hour have been reported. The radiant seems to be located
further west than the position listed by the IMO. A good guess would be the
radiant position listed by Gary Kronk in his book "Comets and Meteors". This
position is 05:40 (085) +52, which places it in northern Auriga, five
degrees northeast of the zero 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.

The Orionids (ORI) are active from a radiant located at 06:08 (092) +15.
This area of the sky is located in northeastern Orion, very close to the
fourth magnitude star Nu Orionis. The radiant is best placed near 04:00
local daylight time, when it lies highest in the sky. Current rates should
be close to five Orionids per hour. The peak activity is predicted to occur
on October 21, with a ZHR near 25. At 66km/sec., the average Orionid is
swift. This shower is seen equally well from both hemispheres.

The Epsilon Geminids (EGE) peak on October 18 with a predicted ZHR of two.
This radiant is currently located at 06:44 (101) +27, which places it in
central Gemini, very close to the third magnitude star Epsilon Geminorum.
The radiant is best placed near 0500 when it lies highest in the sky. At
70km/sec., the average Epsilon Geminid is swift with a high percentage of
persistent trains.

The Northern Apex radiant is now centered at 07:36 (114) +36. This position
lies in southwestern Lynx, five degrees north of the second magnitude star
Castor (Alpha Geminorum). 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 Cancer,
northeastern Gemini, eastern Auriga or southwestern Lynx 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 northwestern 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 07:36 (114) +06. This position lies in Canis Minor, very
close to the zero magnitude star Procyon (Alpha Canis Minoris). 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 northeastern Monoceros, Canis Minor,
southwestern Cancer, western Hydra or southeastern 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 near their annual
peak. 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.

This data is available in tabular form at: 
http://www.amsmeteors.org/lunsford/

Clear Skies!
Robert Lunsford
American Meteor Society