(meteorobs) Meteor Activity Outlook for August 13-19, 2004

[Robert Lunsford]

This week will be another excellent time to view meteor activity. The moon
reaches its new phase on Monday August 16. At this time the moon lies in the
vicinity of the sun and will rise and set with the sun. Therefore it will be
invisible at night and will not interfere with observing. The estimated
total hourly rates for evening observers this week should be near five for
those in the Northern Hemisphere and two for those observers south of the
equator. For morning observers the estimated total hourly rates should be
near thirty for those located in the Northern Hemisphere and fifteen 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 August 14/15. These positions do not change greatly day to day so
the listed coordinates 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.

These are the showers that may be observed this week:

The Kappa Cygnids (KCG) are active from a wide radiant located at 19:00
(285) +59. This position is located in southern Draco, five degrees
northeast of the fourth magnitude star Kappa Cygni. Current rates would be
near one shower member per hour. A large percentage of these meteors are
bright, often fireball class meteors with brilliant colors. With an entry
velocity of 25 km/sec. most of these meteors will appear to travel slower
than average. The radiant is best placed near 2300 Local Daylight Time (11pm
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 North Iota Aquarids (NIA) are active from a radiant currently located at
21:28 (322) -07. This area of the sky is located in western Aquarius, very
close to the position of the third magnitude star Sadalsuud (Beta Aquarii).
Maximum activity occurs on August 19 with an expected ZHR of three. Current
rates would be near one shower member per hour. At 31 km/sec. the NIA's are
of average velocity. This radiant is most active near 0100 LDT when it lies
highest in the southern sky.

The Anthelion radiant is now centered at 22:28 (337) -08. This area of the
sky is located in central Aquarius, three degrees east of the fourth
magnitude star Theta Aquarii Since this radiant is large and diffuse, any
slow to medium speed meteor from eastern Capricornus, southwestern Pegasus,
western Pisces or central Aquarius 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
two shower members per hour  no matter your location.  At this time of year
the Anthelion radiant overlaps both the North Delta Aquarid radiant and the
South Iota Aquarids so distinguishing between these showers will be
difficult but not impossible if you face toward this general area of the
sky.

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. There
is also the possibility that some of this activity may be caused by the
"Jupiter family of comets", comets which have been altered by Jupiter's
gravity into much shorter orbits. 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 anthelions 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. At this time of year the IMO has no designation
for the anthelion radiant as it overlaps several other radiants as it moves
through Capricornus and Aquarius during July and August.

The North Delta Aquarids (NDA) are currently active from a radiant located
at 22:36 (339) -04. This area of the sky is located in northern Aquarius,
three degrees south of the fourth magnitude star Eta Aquarii. This position
is also close to the anthelion 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 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. With maximum activity occurring on
August 8, current hourly rates, seen from the southern tropics, would be
near two per hour.

The South Iota Aquarids (SIA) are active from a radiant currently located at
23:00 (345) -13. This area of the sky is located in central Aquarius, three
degrees northeast of the fourth magnitude star Tau Aquarii. This position is
also very close to the anthelion radiant and without plotting and velocity
estimates, it would be impossible to separate meteors from the two sources.
Maximum activity occurred on August 4 with an expected ZHR of two. Current
rates would be less than one shower member per hour. At 34 km/sec. the SIA's
have virtually the same velocity as the anthelion meteors. This radiant is
most active near 0100 LDT when it lies highest in the southern sky.

The South Delta Aquarids (SDA) are nearing the end of their activity for
2004. The current radiant position lies at 23:28 (352) -12. This area of the
sky is located in eastern Aquarius, four degrees southeast of the fourth
magnitude star Phi Aquarii. The radiant is best positioned near 0300 local
daylight time, when it lies highest in the sky. Expected hourly rates would
be less than one per hour. These meteors encounter the earth at a speed of
41 km/sec. which is a bit faster than average. Activity is best seen from
the Southern Hemisphere where the radiant passes high overhead.

The Perseids (PER) reached an impressive maximum on the morning of August
12. Rates this weekend would be near ten per hour falling to near five later
 in this period. The current radiant position lies at 03:20 (050) +59, which
is located in southwestern Camelopardalis, nine degrees north of the second
magnitude star Mirfak (Alpha 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. At 59km/sec.,
Perseid meteors are usually swift, often exhibiting persistent trains.

The Northern Apex radiant is now centered at 03:28 (052) +34. This position
lies in southern Peresus, seven degrees southeast of the bright variable
star Algol (Beta Persei). This position lies less than thirty degrees south
of the Perseid radiant so those observers who view away from the Perseid
radiant (meaning the Perseid radiant is not visible in their field of view)
have a real chance of including these meteors in their Perseid count.  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 southern Perseus, eastern Andromeda, northwestern
Taurus, northern Aries or Triangulum could be a candidate from this source.
Rates would be now close to three per hour for observers north of the
equator and less than one per hour for those observers south of the equator.

Like the anthelion area, both apex areas are active all year long and travel
approximately one degree eastward per day. Unlike the anthelion 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 03:28 (052) +04. This position lies in extreme southwestern
Taurus, four degrees east of the third magnitude star Menkar (Alpha Ceti).
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 eastern Cetus, southeastern Aries,
northwestern Eridanus or southwestern Taurus could be a candidate from this
source. Rates would now be two per hour regardless of your location.

The Sporadic rates for the Northern Hemisphere are now increasing. One would
expect to see perhaps eight 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 three random meteors can be seen per
hour from the Northern Hemisphere. Rates seen from the Southern Hemisphere
are now lower than those seen in the north with perhaps six random meteors
being seen during the late morning hours and two per hour during the
evening.

Clear Skies!
Robert Lunsford
AMS Operations Manager