(meteorobs) Meteor Activity Outlook for August 10-16, 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 new phase on Sunday August 12. At
this time the moon is located near the sun and is invisible at night. Late
in the period the waxing crescent moon will enter the evening sky but will
not interfere with meteor observing. The estimated total hourly rates for
evening observers this week is near four 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 fifty-five for those located
in the northern hemisphere and twenty 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.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning August 11/12. 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
(284) +58. This position is located in southern Draco, three 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 21:20
(320) -05. This position lies in western Aquarius, two degrees northwest of
the third magnitude star Sadalsuud (Beta Aquarii). The radiant is best
placed near 0100 local daylight time, when it lies highest in the sky.
Current rates would be less than one 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 22:08 (332) -09. This area
of the sky is located in a southwestern Aquarius, two degrees southwest of
the fourth magnitude star Theta Aquarii. 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 regardless of your location. 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 23:20
(350) -13. This position lies in eastern Aquarius, close to the fourth
magnitude star Omega 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 Perseids (PER) reach maximum activity on August 13 with average rates
expected to be near sixty shower members per hour. The current radiant
position lies at 03:04 (046) +58, which is located where the borders of
Perseus, Cassiopeia, and Camelopardalis meet. This position is also three
degrees northwest of the fourth magnitude star Eta Persei. While the radiant
lies above the horizon for most observers in the northern hemisphere, it is
best placed 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 twelve random meteors during the last hour before dawn from
rural observing sites in 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
late morning rates would now be near ten per hour. During the first dark
hour after the end of evening twilight, perhaps two random meteors can be
seen per hour, increasing to five by midnight.

Kappa Cygnid (KCG)  18:52 (284) +58
Northern Hemisphere - 1   Southern Hemisphere - <1

Alpha Capricornid (CAP)  21:20 (320) -05
Northern Hemisphere - <1   Southern Hemisphere - <1

Antihelion (ANT) - 22:08 (332) -09
Northern Hemisphere - 2   Southern Hemisphere - 2

Delta Aquariids (SDA)  23:20 (350) -13
Northern Hemisphere - 1   Southern Hemisphere - 2

Perseids (PER)  03:04 (046) +58
Northern Hemisphere - 40   Southern Hemisphere - 5

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#2007

Clear Skies!
Robert Lunsford
American Meteor Society