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(meteorobs) Meteor Activity Outlook for March 28-April 3, 2003
The moon is new on Tuesday April 1. At this time the moon will be
located in the same part of the sky as the sun and will not interfere
with observing at any time of the night. The estimated total hourly
rates for evening observers this week should be near two for those in
the Northern Hemisphere and 2-3 for those viewing south of the equator.
For morning observers the estimated total hourly rates should be near
eleven for those located in the Northern Hemisphere and twenty two 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.
The positions listed below are exact for Saturday night/Sunday morning
March 29/30 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 13:32 (203) -09. This area of
the sky is located in central Virgo, two degrees northeast of the first
magnitude star Spica (Alpha Virginis). Since this source is large and
diffuse, any slow to medium speed meteor from Virgo could be a candidate
for this shower. The area of the sky 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 2 shower members per hour from all locations.
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 18:32 (278) -08. This position
lies in Scutum, very close to the fourth magnitude star Alpha Scuti.
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 Serpens Cauda 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 18:32 (278) -38. This position lies in northern Corona
Australis, four degrees south of the third magnitude star Eta
Sagittarii. 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 are predicted to peak on March 29 from a radiant located
at 20:40 (310) -63. This area of the sky is located in central Pavo,
three degrees north of the third magnitude star Beta Pavonis. This area
of the sky is too far south to be seen north of the northern equatorial
areas. The rate at maximum is five shower members per hour. These rates
are rarely seen except from far southern locations such as Australia,
South Africa and southern South America. 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 two random meteors 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 2-3 during the evening
hours.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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