(meteorobs) Meteor Activity Outlook for Apr 29-May 5, 2005

[Robert Lunsford]

This upcoming period will see the moon reaching its last quarter phase on
Sunday May 1. At this time the moon rises near 0100 local daylight time and
will be interfering with observations the remainder of the morning. As the
week progresses, the moon will rise later in the morning and its illuminated
portion will decrease as it approached its new phase. The estimated total
hourly rates for evening observers this week should be near two for those in
the Northern Hemisphere and three 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 nine for those in the
Southern Hemisphere. Morning 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 April 30/May 1. 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 15:40 (235) -19. This area of the
sky is located in eastern Libra, seven degrees west of the third magnitude
star Acrab (Beta Scorpii). These meteors were once called the Alpha
Scorpiids, as the radiant is located close to the bright orange star this
time of year. Since this radiant is large and diffuse, any slow to medium
speed meteor from eastern Libra or northwestern Scorpius could be a
candidate for this shower. The center of this area is best placed near 0200
local daylight 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. Observers who send their reports to the
International Meteor Organization (I.M.O.) should label these meteors as
Sagittarids (SAG).

The Beta Corona Australids (CAU) are listed among the radiants of the Dutch
Meteor Society. The current radiant position is located at 17:32 (263) -42.
This area of the sky is located in southeastern Scorpius, two degrees
northwest of the second magnitude star Sargas (Theta Scorpii). The best time
to view this activity is near 0400 local daylight time, when the radiant
lies highest in a dark sky. Rates at maximum activity (May 16) are only
three shower members per hour. Current rates would be still less than one
per hour. Observers in the Southern Hemisphere have an advantage with the
radiant rising much higher in their sky. With an entry velocity of 45
kilometers per second, a majority of these meteors will appear to move at
moderate speeds.

The Eta Aquarids (ETA) are particles from Halley's Comet, which last passed
through the inner solar system in 1986. Even though this is now nineteen
years ago, material is still encountered every year in late April and
throughout most of May. We pass closest to Halley's orbit on May 5. Current
rates would be 1-2 per hour from a radiant located at 22:12 (333) -04. This
area of the sky is located in northern Aquarius, four degrees south of the
third magnitude star Sadalmelik (Alpha Aquarii). The best time to view this
activity is just before the start of morning twilight, when the radiant lies
highest in a dark sky. Observers located closer to the tropics have a better
chance of seeing these meteors as the radiant will rise higher into a dark
sky. Morning twilight is especially troublesome in the high Northern
latitudes, where the radiant is situated low in the sky at the start of
twilight. With an entry velocity of 66 kilometers per second, a majority of
these meteors will appear to move swiftly and produce a high percentage of
persistent trains.

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 dark evening hours perhaps two random
meteors can be seen per hour. Sporadic rates seen from the Southern
Hemisphere are slowly increasing toward a July maximum. From south of the
equator one would expect to see approximately five random meteors per hour
during the late morning hours and three per hour during the evening.  Rates
are reduced during the morning hours for both hemispheres due to moonlight.

Anthelion  (Sagittarids)    15:40 (235) -19
Hourly Rate =     2   N. Hemisphere,    2  S. Hemisphere

Beta Corona Australids (CAU)   17:32 (263) -42
Hourly Rate =    0   N.  Hemisphere,   <1  S. Hemisphere

Eta Aquarids (ETA)   22:12 (333) -04
Hourly Rate =    1   N.  Hemisphere,   2  S. Hemisphere

Clear Skies!
Robert Lunsford
American Meteor Society