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Robert Lunsford - AMS News
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.
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