(meteorobs) Meteor Activity Outlook for July 8-14, 2005

[Robert Lunsford]

This upcoming period will see the moon reaching its first quarter phase on
Thursday July 14. At this time the moon sets near 0100 and will not
interfere with morning observing. This weekend the waxing crescent moon will
set during the evening hours, allowing a good portion of the night to be
used for meteor observing. The estimated total hourly rates for evening
observers this week should be near two for those in the Northern Hemisphere
and three for those observers south of the equator. For morning observers
the estimated total hourly rates should be near eight for those located in
the Northern Hemisphere and twelve 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 9/10. 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 now active from a wide radiant located at
19:16 (289) -15. This position lies in northern Sagittarius, seven degrees
north of the third magnitude star Pi Sagittarii. The radiant is best placed
near 0100 local daylight time, when it lies highest in the sky. Current
rates would be near one per hour. 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. This radiant is located close
to the anthelion radiant this time of year and it may be difficult to
separate the two.

The Anthelion radiant is now centered at 20:08 (302) -19. This area of the
sky is located on the Sagittarius/Capricornus border, six degrees southwest
of the third magnitude star Dabih (Beta Capricorni). Since this radiant is
large and diffuse, any slow to medium speed meteor from eastern Sagittarius,
southern Aquila or western Capricornus 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 hour from the Southern Hemisphere and one from the
Northern.

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. Observers who send their reports to the
International Meteor Organization (I.M.O.) should label these meteors as
Sagittarids (SAG).

The Southern Delta Aquarids (SDA) are now producing a ZHR of one from a
radiant located at 21:40 (325) -19. This position lies in eastern
Capricornus, two degrees south of the fourth magnitude star Gamma
Capricornii. The radiant is best placed near 0400 local daylight time, when
it lies highest in the sky. 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.

The Sporadic rates for the Northern Hemisphere are now 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 two 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 eight random meteors per hour during
the late morning hours and three per hour during the evening.

Alpha Capricornids (CAP)   19:16  (289)  -15
Hourly Rate =    <1  N.  Hemisphere,   1  S. Hemisphere

Anthelion  (Sagittarids)    20:08 (302) -19
Hourly Rate =     1   N. Hemisphere,    2  S. Hemisphere

Southern Delta Aquarids (SDA)   21:40  (325)  -19
Hourly Rate =    <1  N.  Hemisphere,   <1  S. Hemisphere

Clear Skies!
Robert Lunsford
American Meteor Society
http://www.amsmeteors.org/lunsford/