(meteorobs) Meteor Activity Outlook for March 18-24, 2005

[Robert Lunsford]

This upcoming period will see the moon waxing and setting later in the
morning sky with each passing night. The moon will reach its full phase on
Friday March 25.  This weekend would be a good time to view the morning
meteor activity. With each passing night next week, the dark window of
opportunity between moonset and the start of morning twilight becomes
smaller. The estimated total hourly rates for evening observers this week
should be near one 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 six for those located in the Northern Hemisphere
and ten 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 March 19/20. 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 12:52 (193) -05. This area of the
sky is located in central Virgo, ten degrees northwest of the first
magnitude star Spica (Alpha Virginis). Since this radiant is large and
diffuse, any slow to medium speed meteor from Virgo or Corvus 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. Observers who send their reports to the
International Meteor Organization (I.M.O.) should label these meteors as
Virginids (VIR).

The Gamma Normids (GNO) are active from a radiant located at 17:04
(256) -50. This position lies in northwestern Ara, five degrees west of the
third magnitude star Alpha Arae. ZHR's were expected to be near  six at
maximum (March 13). Current rates would only be 1-2 shower members per
hour as seen from the Southern Hemisphere. Due to the far southern
declination of the radiant, this shower is not well seen north of the
northern equatorial regions. This area of the sky is best placed near 0600
local standard time when it lies highest in the sky. At 56 km/sec. the Gamma
Normids normally produce meteors of swift angular velocities.

The Delta Pavonids (DPA) are listed among the radiants of the Dutch Meteor
Society. They are predicted to peak on March 28. The radiant currently lies
at 19:36 (294) -61. This area of the sky is located in northern  Pavo, seven
degrees southwest of the second magnitude star Peacock (Alpha Pavonis). This
area of the sky is too far south to be seen north of the northern equatorial
areas. The rate at maximum is five shower members per hour. These rates are
rarely seen except from far southern locations such as Australia, South
Africa and southern South America. Current hourly rates would be less than
one. The best time to view this activity is just before the start of morning
twilight, when the radiant lies highest in a dark sky. With an entry
velocity of 60 kilometers per second, a majority of these meteors will
appear to move swiftly.

The Sporadic rates for the Northern Hemisphere are now reaching their low
plateau for the year. From now through June morning sporadic rates will
remain near five per hour. During the evening hours perhaps one random
meteor can be seen each hour. Sporadic rates seen from the Southern
Hemisphere are slowing increasing toward a July maximum. From south of the
equator one would expect to see approximately eight random meteors per hour
during the late morning hours and two per hour during the evening. Evening
rates are reduced for each hemisphere due to moonlight.


Anthelion        Radiant Position  = 12:52 (193) -05
Hourly Rate = 1  N. Hemisphere, 1  S. Hemisphere

Gamma Normids (GNO)   Radiant Position  = 17:04 (256) -50
Hourly Rate = 0  N. Hemisphere, 1  S. Hemisphere

Delta Pavonids (DPA)   Radiant Position  = 19:36 (294) -61
Hourly Rate = 0  N. Hemisphere, <1  S. Hemisphere

Clear Skies!
Robert Lunsford
American Meteor Society