Meteor Activity Outlook for July 20-26, 2007

For observers in the northern hemisphere meteor
activity finally picks up in July after months of low rates. Several showers
become active this month and peak toward the end of the month. Sporadic activity
increases with each passing week throughout the northern summer. Activity seen in
the southern hemisphere is peaking and will remain strong throughout the month.
Later in the month strong minor shower activity will offset the falling sporadic
rates in the south. Sporadic rates as seen from the southern hemisphere are
highest early in the month and then fall quite steeply as the southern winter
progresses.

During this period the moon reaches its first quarter
phase on Sunday July 22. At this time the half-illuminated moon is present in the evening sky and
sets near 0100 local daylight time (LDT). Later in the period the waxing gibbous
moon intrudes into the morning sky and limits the dark time between moonset and the
start of morning twilight. The estimated total hourly rates for evening observers this week is near two
for those located north of the equator and three for observers south of the equator.
For morning observers the estimated total hourly rates should be near eighteen for those
located in the northern hemisphere and twenty-four for those viewing from south of
the equator. 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. Evening rates are reduced during this
period due to moonlight.

The radiant positions listed below are exact for Saturday
night/Sunday morning July 21/22. 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. Doing this 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 active from a wide radiant located at 20:04
(301) -12. This position lies in where the borders of Sagittarius, Capricornus and
Aquila meet, three degrees northwest of the third magnitude star Alpha Capricornii.
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. Don’t
mix these meteors with the 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.

The Antihelion (ANT) radiant is now centered at 20:48 (312) -17. This area
of the sky is located in a central Capricornus, four degrees northwest of the fourth
magnitude star Theta Capricornii. 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
per hour as seen in the northern hemisphere and three per hour for those located
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 another center of activity located
at 21:32 (323) -02. This radiant is active during the period July 18-23, from an
area in northern Aquarius. This position lies four degrees southwest of the third
magnitude star Sadalmelik (Alpha Aquarii). Maximum occurs on July 20. This
radiant is best placed near 0200 LDT when it lies highest in the sky. It appears
that seven percent of the total sporadic activity for the night is related to this
radiant. This would only provide 1-2 shower members per hour at best. At 39km/sec.,
the average meteor from this radiant would be of medium velocity.

The Delta Aquariids (SDA) are active from a radiant located at 22:20
(335) -18. This position lies in southwestern Aquarius, ten degrees west of the
third magnitude star Delta Aquarii. The radiant is best placed near 0300 local
daylight time, when it lies highest in the sky. Current rates would be near three
per hour visible from the southern hemisphere and two per hour from the northern
hemisphere. 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 peaks on July 28 with
expected ZHR’s near twenty.

The Pisces Austrinids (PAU) The also peak on July 28, but are much weaker
than the Delta Aquarids. Visual rates rarely exceed three per hour, even
where the radiant passes through the zenith. The radiant is located at 22:24
(336) -33. This area of the sky lies eight degrees southwest of the bright star
Fomalhaut (Alpha Piscis Austrini). These meteors are best seen near 0300
LDT, when the radiant lies highest above the horizon. At 35/km per second, these
meteors are of average velocity, slower than the Aquarids but faster than the
Alpha Caps and the antihelion meteors.

Sirko Molau’s study of video radiants has revealed early Perseid activity peaking
on July 20. The radiant is then located at 00:48 (012) +51, which places it
southern Cassiopeia, six degrees south of the second magnitude star Shedar
(Alpha Cassiopeiae). This radiant is best placed at dawn when it lies highest in
the sky. This enhancement of Perseid meteors is active July 15-22 when rates may
rise to 2-3 per hour. At 52km/sec., the average meteor from this radiant would be
of medium-swift velocity with a good percentage of trains.

Sporadic rates are now rising for observers in the northern hemisphere and
have peaked for those located south of the equator. One would expect to see perhaps
ten random meteors during the last hour before dawn from rural observing sites
located in the northern hemisphere. During the first dark hour after the end of
evening twilight, perhaps two random meteors can be seen per hour. Sporadic rates
increase as the night progresses so rates seen near midnight would be near six
per hour. Late morning sporadic rates seen from the southern hemisphere are now
near fifteen per hour from rural observing sites. During the first dark hour after
the end of evening twilight, perhaps three random meteors can be seen per hour,
increasing to eight by midnight. Evening rates during this period are reduced by
moonlight.

^The main Perseid display peaks on August 13.