(meteorobs) Meteor Activity Outlook for July 20-26, 2007

[Robert Lunsford]

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.

Alpha Capricornid (CAP) 19:36 (294) -14
Northern Hemisphere - 2   Southern Hemisphere - 2

Antihelion (ANT) - 19:52 (298) -19
Northern Hemisphere - 2   Southern Hemisphere - 3

Alpha Aquariids (AAQ)  21:32 (323) -02
Northern Hemisphere - <1   Southern Hemisphere - <1

Delta Aquariids (SDA)  21:56 (329) -19
Northern Hemisphere - 2   Southern Hemisphere - 3

Pisces Austrinids (PAU) 22:24 (336) -33
Northern Hemisphere - <1   Southern Hemisphere - 1

Perseids (PER) July 20^ 00:48 (012) +51
Northern Hemisphere - 3   Southern Hemisphere - <1

^The main Perseid display peaks on August 13.

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#X2007

Clear Skies!
Robert Lunsford
American Meteor Society