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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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