Meteor Activity Outlook for July 5-11, 2008

After several months of low activity the meteor
rates for both hemispheres see a marked increase in July. In the northern hemisphere
the change is not noticeable until mid-month when several southern radiants, the
Perseids, and sporadic rates all increase in activity. Southern rates are good all month long.

During this period the moon reaches its first quarter
phase on Thursday July 10th. At this time the moon will be located ninety degrees
east of the sun and will set near 0100 local daylight time (LDT). This weekend the thin
waxing crescent moon will set during the evening hours and will not interfere with
observing. As seen from the
mid-northern hemisphere (45 N) the estimated total hourly rates during the evening
observers would be near two. For morning observers the estimated total hourly rates
should be near twelve. For those located in the mid-southern hemisphere (45 S) morning
rates would be near twenty and evening rates near four. 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 and rates listed below are exact
for Saturday night/Sunday morning July 5/6. 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. It must
be remembered that meteor activity is rarely seen at the radiant position. Rather
they shoot outwards from the radiant so it is best to center your field of view so
that the radiant lies at the edge and not the center. Viewing there will allow you to
easily trace the path of each meteor back to the radiant (if it is a shower member)
or in another direction if it is a sporadic. 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.

The following showers are expected to be active this week:

The Alpha Capricornids (CAP) are beginning to come alive from a wide radiant
located at 19:04 (286) -16. This position lies in eastern Sagittarius, two degrees
east of the second magnitude star Nunki (Sigma Sagittarii). The radiant is best
placed near 0100 LDT, when it lies on the meridian and is highest in the sky.
Current rates would be less than one per hour, no matter your location. Don’t
confuse these meteors with the more numerous antihelion meteors, which have a
radiant just to the east. Both radiants need to be in your field of view to
properly sort these meteors. 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 large Antihelion (ANT) radiant is now centered at 19:48 (297) -20.
This area of the sky lies in eastern Sagittarius, near the faint star 58 Sagittarii.
Actually any meteor from western Capricornus, southern Aquila, as well as eastern
Sagittarius could be a candidate for this shower. This radiant is best placed near
0200 LDT when it lies on the meridian and is highest in the sky. Rates at this
time should be near two for northern observers and three for observers south of
the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor
would be of medium-slow speed.

Sirko Molau’s study of video radiants has revealed activity during the
period July 8-22, from an area in northwestern Aquarius. The first of two maximums
occurs on July 10 with the radiant located at 21:00 (315) -04. This position lies
five degrees northwest of the third magnitude star Sadalsuud (Beta Aquarii).
This radiant is best placed near 0300 LDT when it lies highest in the sky. Rates
would most likely be less than one shower member per hour no matter your location.
At 40km/sec., the average meteor from this radiant would be of medium velocity.

Sirko Molau’s study of video radiants has revealed another region of activity in
Andromeda that is active from July 2-7. Maximum occurs on July 7 when the
radiant is located at 01:40 (025) +47 This position lies near the fourth magnitude
star 51 Andromedae, which is located near the Perseus/Cassiopeia border. This
radiant is best placed during the last hour of the night when it lies highest in
a dark sky. Rates would most likely be less than one shower member per hour no
matter your location. At 56km/sec., the average meteor from this radiant would be
of swift velocity. These parameters look suspiciously like those of the early
Perseids yet no association is mentioned.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are
finally beginning to increase. One would expect to see approximately nine
random meteors during the last hour before dawn from rural observing sites and
two per hour during the evening hours. As seen from the mid-southern hemisphere
(45S) morning rates would be near seventeen per hour as seen from rural observing
sites and four per hour during the evening hours.

The table below presents a condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning.