(meteorobs) Meteor Activity Outlook for May 7-13, 2004

[Robert Lunsford]

The moon reaches its last quarter phase on Tuesday May 11. At this time the
moon lies ninety degrees west of the sun and will rise near 0100 local
daylight time. This weekend the moon will be a waning gibbous phase and will
be a nuisance for those observing during the morning hours. 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 eight for those in the
Southern Hemisphere. Morning 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 8/9. 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 16:12 (243) -21. This area of the
sky is located in northwestern Scorpius, only one degree east of the fourth
magnitude double star Omega Scorpii. Since this radiant is large and
diffuse, any slow to medium speed meteor from eastern Libra, southwerstern
Ophiuchus 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 north of the equator and two 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 Eta Lyrids are produced by comet IRAS-Araki-Alcock, which passed very
close to the Earth twenty one years ago this May. Weak activity from this
radiant has been seen in most years from May 5 through May 17, with maximum
activity occurring on May 8. The current radiant position is located at
19:16 (289) +44. This area of the sky is located in western Cygnus, nine
degrees northeast of the zero magnitude star Vega (Alpha Lyrae). 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 the intense moonlight this
year, expect to see less than one shower member per hour on the morning of
maximum activity. With an entry velocity of 44 kilometers per second, a
majority of these meteors will appear to move at moderate speeds.

The Beta Corona Australids (CAU) are listed among the radiants of the Dutch
Meteor Society. The current radiant position is located at 18:24 (276) -41.
This area of the sky is located in central Corona Australis, six degrees
south of the second magnitude star Epsilon Sagittarius. 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 still 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 21:12 (318) 00. This position
lies in northwestern Aquarius, seven degrees northwest of the third
magnitude star Sadalsuud (Beta 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 northern
Aquarius, northwestern Capricornus, southern Delphinus, Equuleus or
southwestern Pegasus 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 21:12 (318) -30. This position lies in northeastern
Microscopium, four degrees southeast 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 passed closest to Halley's orbit on May 5.
Current rates would be 1-2 per hour from a radiant located at 22:44 (341)
00. This area of the sky is located in northern Aquarius, two degrees east
of the fourth magnitude star Eta 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 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 four random meteors being seen per hour during the early morning
hours and three per hour during the evening.  Morning rates are reduced
during this period due to moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager