(meteorobs) Meteor Activity Outlook for May 28 - June 3, 2004

[Robert Lunsford]

The moon reaches its full phase on Thursday June 3. At this time the moon
lies in opposition to the sun and will rise as the sun sets and set as the
sun rises. This weekend though the moon will set early enough to allow some
observing before the start of morning twilight. 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. These rates are
reduced due to moonlight. For morning observers the estimated total hourly
rates should be near ten for those located in the Northern Hemisphere and
sixteen 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 radiant positions listed below are exact for Saturday night/Sunday
morning May 29/30. 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 Omega Scorpids (OSC) are listed among the radiants of the Dutch Meteor
Society. I once felt these meteors were part of the antihelion complex but
they now seem to be a separate source. The peak is listed as June 2 with a
ZHR of 5. Actual observed rates would be less unless one lives deep in the
Southern Hemisphere. The current radiant position is 15:44 (236) -20. This
area of the sky is located in eastern Libra, five degrees west of the third
magnitude double star Acrab (Beta  Scorpii). The best time to view this
activity is near midnight, local daylight time, when the radiant lies on the
meridian and is positioned highest in the sky. With an entry velocity of 21
kilometers per second, these meteors will appear to move slowly.

The Antihelion radiant is now centered at 17:32 (263) -23. This area of the
sky is located in southeastern Ophiuchus, two degrees northeast of the third
magnitude star Theta Ophiuchi. Since this radiant is large and diffuse, any
slow to medium speed meteor from southern Ophiuchus, northwestern
Sagittarius, southwestern Serpens Cauda or northern 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 north of the equator
and three per hour for those situated south of the equator.

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 20:08 (302) -39.
This area of the sky is located in southeastern Sagittarius, four degrees
southeast of the fourth magnitude star Theta Sagittarii. The best time to
view this activity is near 0400 local daylight time, when the radiant lies
highest in a dark sky. ZHR's at maximum activity (May 15) were predicted to
be only three shower members per hour so current rates would be far 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 22:32 (338) +07. This position
lies in southwestern Pegasus some four degrees southwest of the third
magnitude star Zeta Pegasi. 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 northern Aquarius,
southern Delphinus, Equuleus or southwestern Pegasus 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 22:32 (338) -23. This position lies in southern Aquarius,
eight degrees northwest of the first magnitude star Fomalhaut (Alpha Piscis
Austrini. 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 southern Aquarius,
southeastern Capricornus, or northern Pisces Austrinus could be a candidate
from this source. Rates would now be one per hour in the Northern Hemisphere
and three per hour in the Southern Hemisphere.

The Sporadic rates for the Northern Hemisphere are still declining. One
would currently expect to see perhaps four 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 six random meteors being seen per hour during the early morning
hours and two per hour during the evening. Evening rates are reduced due to
moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager