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(meteorobs) Meteor Activity Outlook for May 9-15, 2003
The moon reaches its first quarter phase on Friday May 9. This weekend the
moon will set during the early morning hours, still allowing a few hours of
total darkness before the onset of morning twilight. By the middle of next
week the moon will remain in the sky up to the time of morning twilight,
severely hampering any observing. The estimated total hourly rates for
evening observers this week should be near one for northern viewers and two
for those located south of the equator. For morning observers the estimated
total hourly rates should be near ten for those located in the Northern
Hemisphere and eighteen 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. Evening rates are reduced by
moonlight during this period.
The radiant positions listed below are exact for Saturday night/Sunday
morning May 10/11. The positions do not change greatly day to day so they
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 source is now centered at 16:20 (245) -21. This area of the
sky is located in northwestern Scorpius, six degrees northwest of the first
magnitude orange star Antares (Alpha Scorpii). For years these meteors were
known as the Alpha Scorpids this time of year. Since this source is large
and diffuse, any slow to medium speed meteor from northwestern Scorpius or
southern Ophiuchus could be a candidate for this shower. This 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 less than 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 Sagittarids or "SAG".
The Beta Corona Australids are listed among the radiants of the Dutch Meteor
Society. The current radiant position is located at 18:28 (277) -41. This
area of the sky is located in central Corona Australis, six degrees south of
the second magnitude star Iota Epsilon Sagittarii. 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 16) are only three
shower members per hour. Current rates would be near 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 Eta Lyrids are produced by comet IRAS-Araki-Alcock, which passed very
close to the Earth twenty 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 9. The current radiant position is located at
19:04 (286) +44. This area of the sky is located in northeastern Lyra, eight
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. Expect to see perhaps one
shower member per hour on the morning of maximum activity, after the moon
has set. With an entry velocity of 44 kilometers per second, a majority of
these meteors will appear to move at moderate speeds.
The Northern Apex area is now centered at 21:20 (320) +01. This position
lies in northern Aquarius, six 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. Since this source is large and
diffuse any meteors from Equuleus, southern Delphinus, southwestern Pegasus
or northern Aquarius could be a good candidate for this shower. This source
should provide at least 2 meteors per hour no matter your location. Be sure
to be careful to separate these meteors from the nearby Eta Aquarid radiant.
Meteors from both sources would be similar in both appearance and rates.
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 21:20 (320) -29. This position lies in northeastern
Microscopium, seven degrees south of the fourth magnitude star Zeta
Capricornii. 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 northeastern Microscopium, western Pisces Austrinus or southern
Capricornus 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 Eta Aquarids are particles from Halley's Comet, which last passed
through the inner solar system in 1986. Even though this is now seventeen
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 6.
Current rates would be near two shower members per hour from a radiant
located at 22:48 (342) 00. This area of the sky is located in northeastern
Aquarius, three 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 above the horizon in a dark sky.
With an entry velocity of 66 kilometers per second, a majority of these
meteors will appear to move swiftly and produce persistent trains.
The Sporadic rates for the Northern Hemisphere are now slowly declining and
will do so until June. One would expect to see perhaps six 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
also be approximately eight random meteors being seen per hour during the
late morning hours and three during the evening hours. Evening rates are
reduced during this period due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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