(meteorobs) Meteor Activity Outlook for July 29- August 4, 2005

Robert Lunsford lunro.imo.usa at cox.net
Thu Jul 28 16:43:36 EDT 2005


This upcoming period will see the moon waning from a fat crescent phase,
some forty percent illuminated, down to an imperceptible thin crescent. In
the beginning of this period, the moon will be a nuisance with the lunar
glare obscuring the faintest meteors. As the week progresses, the thinning
moon will not be so bothersome. The estimated total hourly rates for evening
observers this week should be near three, no matter your location. For
morning observers the estimated total hourly rates should be near twenty,
again no matter your location. Morning rates are slightly reduced due to
moonlight.  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 30/31. 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 planetariums) 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 latitude. 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 further down the list rise later in the night.

These are the showers that may be observed this week:

The Alpha Capricornids (CAP) are active from a wide radiant located at 20:36
(309) -10. This position lies in northwestern Capricornus, three degrees
west of the fourth magnitude star Epsilon Aquarii. The radiant is best
placed near 0100 local daylight time, when it lies highest in the sky.
Current rates would be near two per hour, no matter your location. With an
entry velocity of 23 km/sec., most activity from this radiant would be slow.
This radiant is well seen except for far northern latitudes where it remains
twilight all night long and the radiant does not rise as high into their
sky.

The Anthelion radiant is now centered at 21:28 (322) -14. This area of the
sky is located in eastern Capricornus, four degrees northwest of the third
magnitude star Nashira (Delta Capricornii). Since this radiant is large and
diffuse, any slow to medium speed meteor from eastern Capricornus or western
Aquarius could be a candidate for this shower. The center of this area 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 no
matter your location.

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.

The North Delta Aquarids (NDA) are currently active from a radiant located
at 21:52 (328) -08. This area of the sky is located in central Aquarius,
eight degrees southwest of the third magnitude star Sadalmelik (Alpha
Aquarii). At 42 km/sec. the NDA's are a bit faster than your average meteor.
This radiant is most active near 0200 LDT when it lies highest in the sky.
Current hourly rates should be near one shower member per hour, no matter
your location. This shower is predicted to peak near August 8 with ZHR's of
four.

The Southern Iota Aquarids (SIA) peak on August 4 with a ZHR of two. With
these low rates one would be lucky to see one shower member per hour. The
radiant is currently located at 21:54 (329) -16. This area of the sky is
located in eastern Capricornus, two degrees east of the third magnitude star
Nashira (Delta Capricornii). This position is close to the antihelion
radiant and without plotting and velocity estimates, it would be impossible
to separate meteors from the two sources. At 34 km/sec. the SIA's have
virtually the same velocity as the antihelion meteors. This radiant is most
active near 0200 LDT when it lies highest in the sky.

The Southern Delta Aquarids (SDA) are active from a radiant located at 22:24
(341) -16. This position lies in western Aquarius, seven degrees west of the
third magnitude star Delta Aquarii. The radiant is best placed near 0400
local daylight time, when it lies highest in the sky. Currently this should
be the most active radiant with rates of 3-5 per hour. With an entry
velocity of 41 km/sec., most activity from this radiant would be of average
velocities. These meteors tend to be faint so the darkest skies are
necessary in order to see this shower well. This shower peaked on July 28.

The Pisces Austrinids (PAU) are currently active from a radiant located at
22:56 (344) -29. This area of the sky lies in eastern Pisces Austrinus, very
close to the first magnitude star Fomalhaut (Alpha Piscis Austrini). This
shower peaked on the July 28 with ZHR's of three. Current rates would be two
per hour as seen from the most favored southern latitudes, where the radiant
rises higher in the sky. From the Northern Hemisphere rates would only be
near one per hour. 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 (PER) activity is now strengthening with each passing night. The
current radiant position lies at 02:04 (031) +55, which is located in
northwestern Perseus, three degrees southwest of the famous "Double Cluster"
(h and x Persei) on most star charts. 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 three per hour. These
rates will gradually increase as we approach the August 12 maximum. At 59
km/sec., Perseid meteors are swift, often exhibiting persistent trains.

The Sporadic rates for the Northern Hemisphere are now quickly rising from
their low plateau for the year. Observers can expect around six random
meteors per hour during the morning hours as seen from locations in the
Northern hemisphere. During the dark evening hours perhaps three random
meteors can be seen per hour north of the equator. Sporadic rates seen from
the Southern Hemisphere are near a secondary annual maximum. From south of
the equator one would expect to see approximately six random meteors per
hour during the late morning hours and three per hour during the evening.
Morning rates are reduced due to moonlight.

Alpha Capricornids (CAP)   20:36 (309) -10
Hourly Rate = N. Hemisphere 2 - S. Hemisphere 2

Anthelion    21:28 (322) -14
Hourly Rate = N. Hemisphere 2 - S. Hemisphere 2

Northern Delta Aquarids (NDA)   21:52 (328) -08
Hourly Rate = N. Hemisphere 1 - S. Hemisphere 1

Southern Iota Aquarids (SIA)   21:54 (329) -16
Hourly Rate = N. Hemisphere 1 - S. Hemisphere 1

Southern Delta Aquarids (SDA)   22:24 (341) -16
Hourly Rate = N. Hemisphere 3 - S. Hemisphere 4

Piscis Austrinids (PAU)   22:56 (344) -29
Hourly Rate = N. Hemisphere 1 - S. Hemisphere 2

Perseids (PER)   02:04 (031) +55
Hourly Rate = N. Hemisphere 3 - S. Hemisphere <1

Clear Skies!
Robert Lunsford
American Meteor Society



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