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(meteorobs) Meteor Activity Outlook for Aug 15-21, 2003
The moon reaches its last quarter phase on Wednesday August 20. At this time
the moon will lie ninety degrees west of the sun and will rise near 0100.
This will cause some minor lunar interference during the most productive
morning hours. The estimated total hourly rates for evening observers this
week should be near four for those in the Northern Hemisphere and two in the
Southern Hemisphere. For morning observers the estimated total hourly rates
should be near fifteen for those located in the Northern Hemisphere and ten
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 reduced due to moonlight.
The radiant positions listed below are exact for Saturday night/Sunday
morning Aug 16/17. 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 Kappa Cygnids (KCG) will reach maximum activity on the 18th from a
radiant is located at 19:00 (285) +59. This position is located in
southeastern Draco some six degrees northwest of the fourth magnitude star
Kappa Cygni. Current rates will be one to two shower members per hour this
week. The radiant is best placed near 2300 (11pm) local daylight time when
it lies on the meridian and highest in the sky. Due to the extreme northern
declination (celestial latitude) the Kappa Cygnids are not well seen south
of the equator. The entry velocity of the Kappa Cygnids is 25 km/sec., which
is slower than your average meteor. This shower is rich in bright meteors.
The North Iota Aquarids (NIA) are currently active from a radiant located at
21:36 (324) -07. This area of the sky is located in western Aquarius only
one degree southeast of the third magnitude star Sadalsuud (Beta Aquarii).
This radiant is most active near 0100 LDT when it lies highest in the sky.
Maximum activity occurs on August 20 with a ZHR of three. Current rates
would be near one shower member per hour. At 31 km/sec. the NIA's are a bit
slower than your average meteor.
The Antihelion radiant is now located at 22:36 (339) -08. This area of the
sky is located in central Aquarius some five degrees east of the fourth
magnitude star Theta Aquarii. Any slow to medium speed meteor from the
northeastern Capricornus, western Pisces or central Aquarius could be a
candidate for this shower. The radiant 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 north of
the equator and three an hour from areas 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.
The North Delta Aquarids (NDA) are currently active from a radiant located
at 22:44 (341) -04. This area of the sky is located in north central
Aquarius, four degrees southeast of the fourth magnitude star Eta Aquarii.
This position is very close to the antihelion radiant. This week, chances
are a meteor from this area would most likely be from the antihelion
radiant. Like the antihelion radiant, the NDA's are most active near 0200
LDT when it lies highest in the sky. With the maximum now more than a week
past, rates would be one shower member per hour or less. At 42 km/sec. the
NDA's are a bit faster than your average meteor.
The South Delta Aquarids (SDA) are near the end of their activity for 2003.
The radiant is currently located at 23:36 (354) -12. This area of the sky is
located in eastern Aquarius, three degrees northeast of the fourth magnitude
star Omega 2 Aquarii. The radiant lies low in the southeastern sky during
the late evening hours and is not well seen until it approaches the meridian
near 0300 LDT. This shower peaked on July 28 so current rates would far less
than one shower member per hour. These meteors encounter the earth at a
speed of 41 km/sec. which is a bit faster than average.
Perseid (PER) activity is now decreasing with each passing night. The
current radiant position lies at 03:04 (046) +58, This position lies in
extreme eastern Cassiopeia, six degrees north of the third magnitude star
Gamma Persei. The radiant is well placed for those in the Northern
Hemisphere during the last few hours before dawn. Due to the high northern
declination (celestial latitude) of the radiant, rates seen from the
Southern Hemisphere are very low or non-existent. Current Perseid rates for
those north of the equator should be near two to four shower members per
hour. At 59 km/sec., Perseid meteors are swift, often exhibiting persistent
trains.
The Northern Apex radiant is now located at 03:36 (054) +34. This position
lies in southern Perseus, three degrees northwest of the fourth magnitude
star Omicron Persei. This area of the sky is best placed for viewing during
the last dark hour before dawn. Since this radiant is diffuse any meteors
from northeastern Aries, southern Perseus or northwestern Taurus could be a
good candidate for this shower. This source should provide at least two
meteors per hour for those in the Northern Hemisphere and less than 1 per
hour for those in the Southern Hemisphere.
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 03:36 (054) +04. This position lies in southwestern Taurus,
five degrees southeast of the fourth magnitude star Omicron Tauri. 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 Cetus,
northwestern Eridanus, southeastern Aries or southwestern Taurus could be a
candidate from this source. Rates would be now close to one per hour
regardless of your location.
The Sporadic rates for the Northern Hemisphere are now rising slowly toward
their peak, which occurs during the last quarter of the year. 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 two random meteors can be seen per hour.
Rates seen from the Southern Hemisphere would be approximately three random
meteors being seen per hour during the late morning hours and two during the
evening hours. Morning rates are reduced for both hemispheres due to
moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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