(meteorobs) Meteor Activity Outlook for October 22-28, 2004

[Robert Lunsford]

This upcoming period will see the moon reaching its full phase on Thursday
October 28. This weekend the waxing gibbous moon will set during the early
morning hours allowing a few hours of dark sky before the onset 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. For morning observers the estimated total
hourly rates should be near twenty for those located in the Northern
Hemisphere and fifteen for those in the Southern Hemisphere. Evening 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 October 23/24. 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 03:04 (046) +17. This area of the
sky is located in eastern Aries, three degrees southwest of the fourth
magnitude star Delta Arietis. Since this radiant is large and diffuse, any
slow to medium speed meteor from eastern 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 Orionids (ORI) are active from a radiant located at 06:28 (097) +16.
This area of the sky is located in western Gemini, two degrees west of the
second magnitude star Alhena (Gamma Geminorum). The radiant is best placed
near 04:00 local daylight time, when it lies highest in the sky. The peak
activity was predicted to occur on October 21, with a ZHR near 25. Current
rates should be close to ten Orionids per hour, falling to five later in
this period. At 66km/sec., the average Orionid is swift. This shower is seen
equally well from both hemispheres.

The Epsilon Geminids (EGE) peaked on October 18 with a predicted ZHR of two.
Current rates would be less than one shower member per hour. This radiant is
currently located at 07:12 (108) +27, which places it in northern Gemini,
three degrees south the fourth magnitude star Tau 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 08:04 (121) +35. This position
lies in southern Lynx, five degrees northeast 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.

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 08:04 (121) +05. This position lies in eastern Canis Minor,
five degrees east of 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 Leo Minorids (LMI) are listed among the radiants of the Dutch Meteor
Society. This is a short lived shower, reaching ZHR's in excess of one for
only three days (October 23-25). Peak ZHR's are two shower members on the
morning of October 24. This radiant is located at 10:48 (162) +37, which
places it in northeastern Leo Minor, three degrees east of the fourth
magnitude star Beta Leo Minoris The radiant is best placed just before dawn
when it lies highest in the sky. At 61km/sec., the average Leo Minorid is
swift.

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