(meteorobs) Meteor Activity Outlook for August 3-9, 2007

[Robert Lunsford]

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.

Kappa Cygnid (KCG)  18:52 (283) +58
Northern Hemisphere - 1   Southern Hemisphere - <1

Alpha Capricornid (CAP)  20:52 (313) -08
Northern Hemisphere - 2   Southern Hemisphere - 2

Antihelion (ANT) - 21:40 (325) -12
Northern Hemisphere - 2   Southern Hemisphere - 3

Delta Aquariids (SDA)  23:00 (345) -14
Northern Hemisphere - 1   Southern Hemisphere - 2

Pisces Austrinids (PAU) 23:12 (348) -27
Northern Hemisphere - <1   Southern Hemisphere - 1

Perseids (PER) 02:28 (037) +56
Northern Hemisphere - 5   Southern Hemisphere - <1

*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