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(meteorobs) Meteor Activity Outlook for Mar 12-18, 2004

The moon reaches its last quarter phase on Saturday March 13. At this time
the moon lies ninety degrees west of the sun and will rise near local
midnight. Observers this weekend will have to contend with bright moonlight
after midnight. As the week progresses the moon will rise later in the
morning providing the observer with more dark skies. The estimated total
hourly rates for evening observers this week should be near two for those in
the Northern Hemisphere and three 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 fourteen for those in the
Southern Hemisphere. Morning rates are reduced 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 March 13/14. 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 12:28 (187) -03. This area of the
sky is located in western Virgo, three degrees southwest of the third
magnitude star Porrima (Gamma Virginis). Since this radiant is large and
diffuse, any slow to medium speed meteor from northern Corvus, western Virgo
or northern Crater 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 two shower
members 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 Virginids (VIR).

The Gamma Normids (GNO) are active from a radiant located at 16:40
(250) -51. This position lies in western Ara, four degrees east of the
fourth magnitude star Gamma Normae. Average ZHR's are near six at maximum
(March 13). Due to the far southern declination of the radiant, this shower
is not well seen north of the northern equatorial regions. This area of the
sky is best placed near 0600 local standard time when it lies highest in the
sky. At 56 km/sec. the Gamma Normids normally produce meteors of swift
angular velocities.

The Northern Apex radiant is now centered at 17:28 (262) -08. This position
lies in eastern Ophiuchus, three degrees west of the fourth magnitude star
Mu Ophiuchi. 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 eastern Ophiuchus, southern Serpens
Cauda, or western Scutum could be a candidate from this source. Rates would
be now close to two 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 17:28 (262) -38. This position lies in the southeastern
Scorpius, very close to the two bright stars outlining the "stinger" of the
scorpion. These stars are also known as "cat eyes" and Lambda and Nu
Scorpii. 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 northwestern Corona
Australis, southwestern Sagittarius or southeastern Scorpius could be a
candidate from this source. Rates would now be less than one per hour in the
Northern Hemisphere and two per hour in the Southern Hemisphere.

The Delta Pavonids (DPA) are listed among the radiants of the Dutch Meteor
Society. They are predicted to peak on March 28. The radiant currently lies
at 19:04 (286) -60. This area of the sky is located in western Pavo, ten
degrees southwest of the second magnitude star Peacock (Alpha 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. Current hourly rates would be less than
one. 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 declining. One would
currently expect to see perhaps two 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 two random meteors 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 six
random meteors being seen per hour during the early morning hours and three
per hour during the evening. Morning rates are reduced due to moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager

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