(meteorobs) Meteor Activity Outlook for August 17-23, 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 first quarter phase on Monday August
20. At this time the half illuminated moon is located ninety degrees east of
the sun and sets near 0100 local daylight time. 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 twelve 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 by moonlight.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning August 18/19. 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. Viewing there 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 19:04
(286) +59. This position is located in southern Draco, seven degrees
northwest of the fourth magnitude star Kappa Cygni. Current rates would be
near two shower members 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 2100 Local Daylight Time (9 pm 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.

Sirko Molau's study of the IMO's video database has led to the discovery of
an active radiant in Capricornus this week. The shower peaks on August 22
from a radiant located at 20:24 (306) -11. This position lies in
northwestern Capricornus, just two degrees northeast of the fourth magnitude
star Alpha Capricornii. The radiant is best placed near 2300 (11pm) local
daylight time, when it lies highest in the sky. Current rates would mostly
likely be less than one per hour, but this is uncertain. With an entry
velocity of only 19km/sec., activity from this radiant would be slow.

The Antihelion (ANT) radiant is now centered at 22:36 (339) -07. This area
of the sky is located in a northern Aquarius, two degrees southwest of the
faint star Kappa 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 barely active from a radiant located at 23:40
(355) -11. This position lies in eastern Aquarius, four degrees northwest of
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 less than one per hour no matter your location. With an entry
velocity of 41 km/sec., most activity from this radiant would be of average
velocities.

Sirko Molau's study of the IMO's video database has led to the discovery of
an active radiant in Cassiopeia this week. The shower peaks on August 26
from a radiant located at 02:20 (035) +62. This position lies in eastern
Cassiopeia, three degrees southeast of the third magnitude star Epsilon
Cassiopeiae. The radiant is best placed near 0500 local daylight time, when
it lies highest in the sky. Current rates would mostly likely be less than
one per hour, but this is uncertain. With an entry velocity of 50 km/sec.,
most activity from this radiant would be of medium-swift velocities.

The Perseids (PER) reached maximum activity on August 13. Rates are now
falling but the activity is still noticable. The current radiant position
lies at 03:44 (056) +58, which is located in southwestern Camelopardalis,
eight northeast of the second magnitude star Mirfak (Alpha Persei). While
the radiant is circimpolar 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. As seen from the southern hemisphere late morning rates would now
be near eight per hour. During the first dark hour after the end of evening
twilight, perhaps two random meteors can be seen per hour. Evening rates are
reduced by moonlight.

Kappa Cygnid (KCG) 18:52 (284) +58
Northern Hemisphere - 2   Southern Hemisphere - <1

August Capricornids (ACP)  20:24 (306) -11
Northern Hemisphere - <1   Southern Hemisphere - <1

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

Delta Aquariids (SDA)  23:40 (355) -11
Northern Hemisphere - <1   Southern Hemisphere - <1

Epsilon Cassiopeids (ECA)  02:20 (035) +62 50
Northern Hemisphere - <1   Southern Hemisphere - <1

Perseids (PER)  03:44 (056) +58 59
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#2007

Clear Skies!
Robert Lunsford
American Meteor Society