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(meteorobs) Meteor Activity Outlook forJuly 25-31, 2003

The moon reaches its new phase on Tuesday July 29. At this time the moon
will lie in the vicinity of the sun as seen from Earth and will not
interfere at all with meteor observing. The estimated total hourly rates for
evening observers this week should be near three regardless of you latitude.
For morning observers the estimated total hourly rates should be near twenty
five for those located in the Northern Hemisphere and thirty 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 July 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 Alpha Capricornid radiant is located at 20:20 (305) -11. This position
is located in northwestern Capricornus, only one degree north of the fourth
magnitude double star Alpha Capricornii. The broad maximum occurs on July 30
with a ZHR of four. The velocity of the Alpha Caps is 25 km/sec., which is
slower than your average meteor. The radiant is best placed near 0100 local
daylight time when it lies on the meridian. The Alpha Caps are known for
their brightly colored fireballs. One should be careful when determining
shower association as the antihelion source lies approximately fifteen
degrees to the northeast.

The Alpha Cygnids are listed as the Psi Cygnids in the list of radiants
published by the Dutch Meteor Society. No matter what you call them they are
often overlooked by the many other better known radiants active at this
time. This radiant was well represented in the studies coordinated by Dr.
Peter Jenniskens between 1980 and 1991. Their studies indicate a ZHR near 3
at maximum activity on July 19. The radiant position is currently located at
20:40 (310) +49. This position is located in northern Cygnus, four degrees
north of the bright star Deneb (Alpha Cygni). With an entry velocity of 37
km/sec. these meteors are of average velocity. The radiant is best placed
near 0200 LDT when it lies nearly overhead for much of the Northern
Hemisphere. Due to its high northern declination this activity is not well
seen from the Southern Hemisphere.

The Antihelion radiant is now located at 21:16 (319) -15. This area of the
sky is located in eastern Capricornus only two degrees northwest of the 4th
magnitude star Iota Capricorni. Any slow to medium speed meteor from the
eastern half of Capricornus or western 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 South Iota Aquarids reach ZHR's of one on July 25. This shower peaks on
August 4 so current rates would be quite low, certainly less than one shower
member per hour. The radiant is currently located at 21:40 (325) -17. This
area of the sky is located in eastern Capricornus, very close to the fourth
magnitude star Gamma Capricornii. This position is also very close to the
antihelion radiant and without plotting and velocity estimates, it would be
impossible to separate meteors from the two sources. This week, chances are
any active At 34 km/sec. the SIA's have virtually the same velocity as the
antihelion meteors. This radiant is most active near 0100 LDT when it lies
highest in the southern sky.

The North Delta Aquarids are currently active from a radiant located at
21:40 (325) -08. This area of the sky is located in western Aquarius, two
degrees southeast of the third magnitude star Sadalsuud (Beta Aquarii). This
position is also close to the antihelion radiant and care must be taken to
distinguish meteors from these sources. At 42 km/sec. the NDA's are a bit
faster than the antihelion meteors. This radiant is most active between 0200
and 0300 LDT when it lies highest in the southern sky. Like many of the
radiants active this time of year the NDA's are better seen from areas south
of the northern tropics or 30 degrees north latitude. Maximum hourly rates,
seen from the southern tropics, are currently two per hour.

The South Delta Aquarids are currently active from a radiant located at
22:36 (339) -17. This area of the sky is located in southern Aquarius, four
degrees southeast of the brilliant planet Mars. 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. Rates would be near 15-20 per hour as
seen from favored southern locations, 5-10 per hour from north temperate
areas and less than five per hour from higher northern latitudes. These
meteors encounter the earth at a speed of 41 km/sec. which is a bit faster
than average. These meteors are also better seen from the Southern
Hemisphere where the radiant passes high overhead.

The Pisces Austrinids are currently active from a radiant located at 22:40
(340) -30. This area of the sky lies in eastern Pisces Austrinus, only three
degrees west of the first magnitude star Fomalhaut (Alpha Piscis Austrini).
This shower peaks on the 28th with ZHR's of five. This shower is also best
seen from Southern latitudes, where the radiant rises much higher in the
sky. These meteors are best seen near 0300 LDT, when the radiant lies
highest above the horizon. These meteors are of average velocity, slower
than the Aquarids but faster than the Alpha Caps and the antihelion meteors.


Perseid activity is now starting and will strengthen slightly with each
passing night. The current radiant position lies at 01:40 (025) +54, which
is located in extreme southwestern Perseus, ten degrees southeast of Shedar
(Alpha Cassiopeiae). 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 per hour. These rates will
gradually increase as we approach the August 13 maximum. At 59 km/sec.,
Perseid meteors are swift, often exhibiting persistent trains.

The Northern Apex radiant is now located at 02:16 (034) +28. This position
lies in southeastern Triangulum, seven degrees northeast of the second
magnitude star Hamal (Alpha Arietis). 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, southwestern Perseus or
southeastern Triangulum could be a good candidate for this shower. This
source should provide at least three 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 02:16 (034) -02. This position lies in north-central Cetus,
less than a degree north of the famous variable star Mira (Omicron Ceti),
which is currently at fourth magnitude. 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 north-central Cetus, northwestern
Eridanus or southwestern Pisces could be a candidate from this source. Rates
would be now close to two 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 also be approximately six
random meteors being seen per hour during the late morning hours and two
during the evening hours.

Clear Skies!
Robert Lunsford
AMS Operations Manager

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