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(meteorobs) Meteor Activity Outlook for April 27-May 3, 2001



The moon reaches its first quarter phase on Monday April 30. This will
still allow morning observers to watch in dark skies this weekend. Since
the moon will be bright during the maximum of the Eta Aquarids I would
suggest that you try to see some of this activity this upcoming week.
The estimated total hourly rates for evening observers this week should
be near 1 for both Northern Hemisphere and Southern Hemisphere
observers. Rates are reduced this week due to moonlight. For morning
observers the estimated total hourly rates would be near 9 for the
Northern Hemisphere and 15 for those located 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 for meteor activity. The positions
listed below are exact for Saturday night/Sunday morning April 28/29.
The positions do not change greatly day to day so these positions may be
used during this entire period.

The Antihelion radiant is now located at 15:32 (233) -18. This area of
the sky is located in eastern Libra near the Scorpius border. Any slow
to medium speed meteor from Libra, northwestern Scorpius, or southern
Serpens Caput may be a good candidate for this shower. This area of the
sky is best placed near 0200 local daylight time (0100 local standard
time) when it lies on the meridian. At this time expect to see perhaps 1
per hour from locations in the Northern Hemisphere and 2 meteors per
hour from the Southern Hemisphere. Unlike most of the annual showers the
antihelion radiant is produced by debris from unknown sources orbiting
in a direct motion like the earth. These sources are most likely
asteroids, which produce stony and metallic debris whose density is much
greater that produced by comets. This debris 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 radiant
is active all year from an area of the sky nearly opposite that of the
sun. The radiant will travel approximately one degree eastward per day
and travels through many different constellations over the course of a
year. It is easiest to simply list these meteors as "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. For instance those who share reports
with the IMO should now label these meteors as Sagittarids (SAG).

The Northern Apex radiant is now located at 20:32 (308) -03. This
position lies on the Aquila/Aquaruis border near the faint star 70
Aquilae. This is fairly close to the Eta Aquarid radiant which lies
slightly to the east. It could be difficult to separate these two
radiants especially if the meteor travels due west. Both radiants
produce meteors with similar characteristics. During this week the Eta
Aquarid radiant would be the stronger source of activity. This area of
the sky is best placed for viewing during the last dark hour before 
dawn. Since this radiant is diffuse any meteors from southeastern
Aquila, northeastern Sagittarius, northwestern Capricornus, western
Aquarius, or southern Delphinus could be a good candidate. As seen 
from the Northern Hemisphere this source should produce at least 1
meteor per hour during the last few hours before dawn. Rates seen from
the Southern Hemisphere should be better with perhaps 2 of these meteors
being seen per hour. Like the antihelion radiant both apex radiants are
active all year long and travel approximately one degree eastward per
day. Unlike the antihelion 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. There are meteors with a
zero inclination that radiate precisely from the apex point on the
ecliptic, exactly 90 degrees west of the sun. These meteors are rare
though as the earth orbits the sun it "sweeps clean" much of the
material that shares the same orbit. Much more debris 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. Meteors from both branches are normally included in the
sporadic count but should also be noted in some manner as to which
branch of the apex complex they appear to radiate.

The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 20:32 (308) -33. This position lies in western
Microscopium south of Capricornus. Like the northern apex these meteors
are best seen toward dawn when the radiant lies highest above the
horizon in a dark sky. Any meteor from  southeastern Sagittarius,
Microscopium, or southern Capricornus could possibly be a candidate from
this source. As seen from the Northern Hemisphere this source now lies
so low in the southeastern sky that chances are little or no activity
will be seen. With the radiant being situated much higher in the sky,
rates seen from the Southern Hemisphere should be better with perhaps
2-3 of these meteors being seen per hour.

The Eta Aquarids are becoming more active as we approach their May 5
maximum.  As stated above, see them now as the May 5 maximum coincides
with the full moon. Current rates are most likely 2-3 per hour during
the last hour before morning twilight. The radiant position lies at
22:08 (332) -04. This area of the sky is located in north central
Aquarius 3 degrees south of the 3rd magnitude star Alpha Aquarii. This 
shower is difficult to see north of 45 degrees north latitude as the
radiant does not rise very high before the beginning of morning
twilight. The north and south tropical areas as well as Australia and
Southern Africa enjoy the best view of this shower. These meteors have a
geocentric velocity of 66 km/sec., which means they would appear to move
slowly if seen near the radiant or near the horizon. If seen far from
the radiant and high in the sky then they would appear to move swiftly.
The Eta Aquarids also produce a high percentage of persistent trains.

The Sporadic rates for the Northern Hemisphere are now in decline and
will do so until June. One would expect to see perhaps 5 random meteors
per hour during the last hours before dawn from rural observing sites.
During the evening hours perhaps 1 random meteor can be seen per hour
with interference from moonlight. Rates seen from the Southern
Hemisphere would now be slightly better than those seen in the Northern
Hemisphere with perhaps 6 random meteors being seen per hour during the
late morning hours and 1 per hour during the evening.

Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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