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(meteorobs) Meteor Activity Outlook for April 30-May 6, 2004

The moon reaches its full phase on Tuesday May 4. At this time the moon
lies opposite of the sun in the sky and will rise as the sun sets and set as
the sun rises. Early in this period one may view under adequate conditions
late in the morning when the moon is low and morning twilight has yet to
begin.  This is also a good time to view the two bright comets visible in
the eastern sky. The estimated total hourly rates for evening observers this
week should be near one for those in the Northern Hemisphere and two for
those south of the equator. For morning observers the estimated total hourly
rates should be near six for those located in the Northern Hemisphere and
eight for those in the Southern Hemisphere. Rates are reduced during this
period 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 May 1/2. The radiants do not change greatly day to day so the given
positions may be used during this entire period. Most star atlases
(available at science stores and libraries) 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 location. 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 last rise later in the night. This list also
provides the order of ascending velocity for each radiant with those listed
first usually being much slower than those last on the list. Velocity should
not be the prime factor for shower association as all showers can produce
slow meteors. Slow meteors can be produced from normally swift showers, such
as the Leonids, when meteors appear near the radiant or close to the
horizon. The true velocity is only revealed in shower members seen far from
the radiant and high in the sky.

The Antihelion radiant is now centered at 15:44 (236) -19. This area of the
sky is located in eastern Libra, five degrees northwest of the second
magnitude star Dschubba (Delta Scorpii). Since this radiant is large and
diffuse, any slow to medium speed meteor from Libra or western Scorpius
could be a candidate for this shower. The center of this area is best placed
near 0100 local standard time when it lies on the meridian and is highest in
the sky. At this time expect to see one shower member per hour regardless of
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. 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 antihelions 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. Those who send their data to the International Meteor Organization
should call these meteors Sagittarids (SAG).

The Beta Corona Australids (CAU) are listed among the radiants of the Dutch
Meteor Society. The current radiant position is located at 17:44 (266) -41.
This area of the sky is located in southeastern Scorpius, two degrees south
of the third magnitude star Kappa 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 15) are only three shower members
per hour. Current rates would be 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 Northern Apex radiant is now centered at 20:44 (311) -02. This position
lies in western Aquarius, two degrees west of the faint star 71 Aquarii.
This area of the sky is best placed for viewing during the last dark hour
before dawn when it lies highest in the sky. Since this radiant is large and
diffuse, any meteor from western Aquarius, northwestern Capricornus,
southern Delphinus, Equuleus or Aquila could be a candidate from this
source. Rates would be now close to one per hour regardless of your
location.

Like the antihelion area, both apex areas 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. This is
not really a "shower" per se, but an artificial radiant created by the
Earth's motion through space. Meteors from both branches are normally
included in the sporadic count. I feel it is a worthy project to see if it
is possible to distinguish these meteors from the normal sporadic
background. On rare occasions there are meteors with a zero inclination that
radiate precisely from the apex point on the ecliptic, exactly 90 degrees
west of the sun. In simplistic terms, these meteors are seldom seen since
the Earth "sweeps clean" much of the material that shares the same orbit as
our planet. Much more material 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.

The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 20:44 (311) -32. This position lies in northern Microscopium,
four degrees south of the fourth magnitude star Omega Capricornii. Like the
northern apex, these meteors are best seen toward dawn when the radiant lies
highest above the horizon in a dark sky. Since this radiant is also large
and diffuse, any meteor from Microscopium, southern Capricornus, western
Pisces Austrinus or southeastern Sagittarius could be a candidate from this
source. Rates would now be less than one per hour in the Northern Hemisphere
and one per hour in the Southern Hemisphere.

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 eighteen
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. At that
time Eta Aquarid rates can reach 30 shower members per hour as seen from the
northern tropical areas southward. Current rates would be 1-2 per hour from
a radiant located at 22:16 (334) -03. This area of the sky is located in
northern Aquarius, two degrees southwest of the fourth magnitude star Gamma
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. With an entry
velocity of 66 kilometers per second, a majority of these meteors will
appear to move swiftly.

The Sporadic rates for the Northern Hemisphere are declining. One would
currently expect to see perhaps three random meteors per hour during the
last hours before dawn from rural observing sites. This estimate and the
morning estimate for the Southern Hemisphere do not include the apex meteors
listed above. During the evening hours perhaps one random meteor can be seen
per hour from the Northern Hemisphere. Rates seen from the Southern
Hemisphere are now stronger than those seen in the northern skies with
perhaps four random meteors being seen per hour during the early morning
hours and two per hour during the evening.  Rates are reduced during this
period due to moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager

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