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(meteorobs) Meteor Activity Outlook for May 11-17, 2001
The moon reaches its last quarter phase on Tuesday May 15. This opens up
a window of opportunity to begin observing again since the moon would be
much less of a hindrance than it was last week. The moon will still be
somewhat of a problem this upcoming weekend so if you are limited to
just weekend watching it may be better to wait until May 19/20, when the
moon will be a very thin waning crescent. The estimated total hourly
rates for evening observers this week should be near 1 for those in
Northern Hemisphere and 2 for Southern Hemisphere observers. For morning
observers the estimated total hourly rates would be near 6 for the
Northern Hemisphere and 9 for those located in the Southern Hemisphere.
These rates assume that you are watching from rural areas away from all
sources of light pollution except for the moon. 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 May 12/13. 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 16:28 (247) -21. This area of
the sky is located in extreme southwestern Ophiuchus where the faint
star Omega Ophiuchi lies. A more helpful guide may be the brilliant
orange star Antares, which lies just 5 degrees to the south. For this
reason the antihelion meteors of May have often been referred to as the
Alpha Scorpids. Any slow to medium speed meteor from Libra,
northwestern Scorpius, southwestern Ophiuchus, 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 Beta Corona Australids is listed among the radiants of the Dutch
Meteor Society. They reach maximum activity on Wednesday May 16. The
current radiant position lies at 18:40 (280) -40. This position lies in
central Corona Australis 2 degrees south of the 4th magnitude star
Lambda Coronae Australis. Due to the low southern declination this
shower is limited to observers in the tropics and the Southern
Hemisphere. The radiant lies highest in the sky near 0430 local daylight
time. ZHR's for this shower are only 3 so don't expect to see much, if
any activity, from this radiant. This is especially true if you live
north of the equator. At 45 km/sec. members of this shower would be of
medium velocity unless seen near the radiant or the horizon.
The Northern Apex radiant is now located at 21:28 (322) +01. This
position lies in northern Aquarius 7 degrees north of the third
magnitude star Sadalsuud (Beta Aquarii). This is fairly close to the Eta
Aquarid radiant which lies 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 still 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 northern Aquarius, Equuleus, or southwestern Pegasus 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 similar. 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 21:28 (322) -29. This position lies in eastern Pisces
Austrinis close to the borders of Microscopium and 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 Pisces
Austrinis, Microscopium, southeastern Capricornus, northwestern Grus,
or southwestern Aquarius 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 reached maximum activity on May 5. Rates are now
declining but 2-3 shower members can still be seen during the last hour
before dawn. The radiant position lies at 22:56 (344) +02. This area
of the sky is located in extreme western Pisces near the borders of
Aquarius and Pegasus. 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 3 random meteors
per hour during the last hours before dawn from rural observing sites.
Rates are low due to moonlight. During the evening hours perhaps 1
random meteor can be seen per hour. Rates seen from the Southern
Hemisphere would now be slightly better than those seen in the Northern
Hemisphere with perhaps 4 (again reduced by moonlight) random meteors
being seen per hour during the late morning hours and 2 per hour during
the evening.
Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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