Meteor Activity Outlook for August 3-9, 2007

August is the best month for viewing meteor
activity from the northern hemisphere. Not only is the activity enjoyable but
the balmy nights are much more pleasant than those experienced later in the year.
As the month begins the southern radiants are still active and often matching the
sporadic rates. The sporadic rates increase as the month progresses providing a
decent show for the normally slow evening hours. The Perseids kick
into high gear the second week of the month and fill the skies with colorful
streaks of light during the entire night. From the southern hemisphere activity
falls precipitously. This is much like what the northern hemisphere experiences
moving from January into February. The southern radiants put on a good show the
first week of the month. They taper off the second week and are nearly extinct by
the third. In the meantime the sporadic rates that were so impressive in early
July are now half as strong and still getting weaker. Unless you are located
near the equator you will not see much of the Perseids. From the southern
hemisphere any evening Perseids are impossible to see. You have to wait until
the last hours before dawn and hope that some will shoot upwards from low in the
northern sky.

During this period the moon reaches its last quarter
phase on Sunday August 5. At this time the half-illuminated moon rises near 0100
local daylight time and remains in the sky the remainder of the night. Conditions
improve as the week progresses with the moon’s phase waning and it rising later in
the morning. The estimated total hourly rates for evening observers this week is near three
for those located north of the equator and two for observers south of the equator.
For morning observers the estimated total hourly rates should be near twenty for those
located in the northern hemisphere and sixteen 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. Morning rates are reduced during this
period due to moonlight.

The radiant positions listed below are exact for Saturday
night/Sunday morning August 4/5. 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 Kappa Cygnids (KCG) are active from a wide radiant located at 18:52
(283) +58. This position is located in southern Draco, four degrees
northwest of the fourth magnitude star Kappa Cygni. Current rates would be
near one shower member per hour. With an entry
velocity of 25 km/sec. most of these meteors will appear to travel slower
than average. The radiant is best placed near 2300 Local Daylight Time (11pm
LDT) when it lies nearly overhead for much of the Northern Hemisphere. Due
to its high northern declination this activity is not well seen from the
Southern Hemisphere.

The Alpha Capricornids (CAP) are active from a wide radiant located at 20:52
(313) -08. This position lies in southwestern Aquarius, two degrees south 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. 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 21:40 (325) -12. This area
of the sky is located in a northeastern Capricornus, three degrees northwest of the
variable star Delta 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.

The Delta Aquariids (SDA) are active from a radiant located at 23:00
(345) -14. This position lies in southwestern Aquarius, two 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 two
per hour visible from the southern hemisphere and one per hour from the northern
hemisphere. With an entry velocity of 41 km/sec., most activity from this radiant
would be of average velocities.

The Pisces Austrinids (PAU) radiant is located at 23:12 (348) -27. This
area of the sky lies in extreme northwestern Sculptor, four degrees northeast of
the bright star Fomalhaut (Alpha Piscis Austrini). These meteors are best seen near
0300 LDT, when the radiant lies highest above the horizon. One can expect rates
near one per hour from the southern hemisphere and less than one from the north.
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.

Perseid (PER) activity is now near five per hour, as seen from the northern
hemisphere. These rates will increase sharply as we approach the peak on the
morning of August 13. The current radiant position lies at 02:28 (037) +56,
which is located in extreme northwestern Perseus, two degrees west of the
fourth magnitude star Eta Persei. 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 when compared to those seen north
of the equator. At 59 km/sec., Perseid meteors are swift, often exhibiting
persistent trains.

Sporadic rates are now rising for observers in the northern hemisphere and
falling steadily for those located south of the equator. One would expect to see perhaps
eight random meteors during the last hour before dawn from rural observing sites
no matter your geographical location. As seen from the northern hemisphere during
the first dark hour after the end of evening twilight, perhaps three 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. As seen from the southern hemisphere during
the first dark hour after the end of evening twilight, perhaps two random meteors
can be seen per hour, increasing to six by midnight. Morning rates for all locations
during this period are reduced by moonlight.