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(meteorobs) Meteor Activity Outlook for April 4-10, 2003



The moon reaches its first quarter phase on Wednesday April 9. At this time
the moon will be located ninety degrees east of the sun and will set near
0100 local daylight time. This will allow good views of the morning activity
this week. The estimated total hourly rates for evening observers this week
should be near one for those in the Northern Hemisphere and 1-2 for those
viewing south of the equator. For morning observers the estimated total
hourly rates should be near ten for those located in the Northern Hemisphere
and twenty for those 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
meteor activity. Rates seen during the evening hours are reduced due to
moonlight.

The positions listed below are exact for Saturday night/Sunday morning April
5/6. The positions do not change greatly day to day so these 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 radiants below are listed in a west to east manner in order
of right ascension (celestial longitude). The radiants 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 following radiants will be active this week:

The Antihelion source is now centered at 14:00 (210) -12. This area of the
sky is located in southeastern Virgo, twelve degrees northwest of the third
magnitude star Zubenelgenubi (Alpha Librae). Since this source is large and
diffuse, any slow to medium speed meteor from southeastern Virgo or western
Libra could be a candidate for this shower. The area of the sky is best
placed near 0200 local daylight time when it lies on the meridian and is
highest in the sky.  At this time expect to see two shower members per hour
from locations south of the equator and perhaps one per hour from locations
further north.

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 share their reports with the I.M.O. should call these
meteors Virginids or "VIR".

The Northern Apex area is now centered at 19:00 (285) -08. This position
lies in southern Aquila, two degrees southwest of the fourth magnitude star
Lambda Aquilae. This area of the sky is best placed for viewing during the
last dark hour before dawn. Since this source is large and diffuse any
meteors from southern Aquila, northeastern Sagittarius or Scutum could be a
good candidate for this shower. This source should provide at least 2
meteors per hour no matter 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 19:00 (285) -38. This position lies in northeastern Corona
Australis, two degrees west of the fourth magnitude star Alpha Coronae
Australis. 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 Corona Australis or southern Sagittarius could a candidate from this
source. Rates should be near 3 per hour from the Southern Hemisphere and
less than 1 per hour from the Northern Hemisphere.

The Delta Pavonids are listed among the radiants of the Dutch Meteor
Society. They were predicted to peak on March 29 with a ZHR of five. The
current radiant position is located at 21:24 (321) -65. This area of the sky
is located in eastern Pavo, very close to the fourth magnitude star Gamma
Pavonis. This area of the sky is too far south to be seen north of the
northern equatorial areas. Current rates as seen from far southern locations
such as Australia, South Africa and southern South America should be 1-2
shower members per hour. 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 60 kilometers per second, a majority of these
meteors will appear to move swiftly.

The Sporadic rates for the Northern Hemisphere are now slowly declining and
will do so until June. One would expect to see perhaps seven random meteors
per hour during the last hours before dawn from rural observing sites. This
estimate and the estimate for the Southern Hemisphere does not include
meteors from the apex radiants. During the evening hours perhaps one random
meteor can be seen per hour. Rates seen from the Southern Hemisphere would
be approximately twelve random meteors being seen per hour during the late
morning hours and 1-2 during the evening hours. Rates seen during the
evening hours are reduced due to moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager

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