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(meteorobs) Meteor Activity Outlook for April 25-May 1, 2003
The moon is new on Thursday May 1. This weekend the moon will be a waning
crescent, rising late in the morning. It will cause slight interference to
observers, but the situation improves with each passing morning as the moon
wanes and rises later each morning. The estimated total hourly rates for
evening observers this week should be near three for northern viewers and
four for those located south of the equator. For morning observers the
estimated total hourly rates should be near 3 for those located in the
Northern Hemisphere and 5 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. Morning rates are slightly reduced
by moonlight during this period.
The radiant positions listed below are exact for Saturday night/Sunday
morning April 26/27. 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 15:24 (231) -18. This area of the
sky is located in southeastern Libra, ten degrees southeast of the third
magnitude star Zubenelgenubi (Alpha Librae). Since this source is large and
diffuse, any slow to medium speed meteor from northwestern Scorpius or Libra
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 Lyrids peaked on April 22 and activity is now dwindling. Current rates
would only be one shower member per hour from a radiant located at 18:24
(276) +34. This area of the sky is located in southwestern Lyra, five
degrees south 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 an entry velocity of 49 kilometers
per second, a majority of these meteors will appear to move swiftly.
The Northern Apex area is now centered at 20:24 (306) -03. This position
lies in extreme southeastern Aquila, three degrees east of the third
magnitude star Theta Aquilae. 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 southeastern Aquila, southern Delphinus or
western Aquarius could be a good candidate for this shower. This source
should provide at least 1 meteor 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 20:24 (306) -33. This position lies in a remote area of
southeastern Sagittarius, not far from the border it shares with
Microscopium. 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 Microscopium or southeastern Sagittarius could a candidate from
this source. Rates should be near 2 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 pass closest to Halley's orbit on May 6. At that
time Eta Aquarid rates can reach 30 shower members per hour as seen from the
northern tropical areas southward. Current rates would be 1-2 per hour from
a radiant located at 22:00 (330) -05. This area of the sky is located in
northern Aquarius, five degrees south of the third magnitude star Sadalmelik
(Alpha 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 now slowly declining and
will do so until June. One would expect to see perhaps five 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 three
random meteors can be seen per hour. Rates seen from the Southern Hemisphere
would be approximately seven random meteors being seen per hour during the
late morning hours and four during the evening hours. Morning rates are
slightly reduced during this period due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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