(meteorobs) Meteor Activity Outlook for August 9-15, 2008

[Robert Lunsford]

Meteor activity kicks into high gear in August as seen from the northern
hemisphere. The main reason for all this activity is the Perseid shower that
peaks on August 12. The shower is active most of the month and remains above
the level of the sporadic background for a week centered on August 12. The
sporadic activity is also increasing as seen from the northern hemisphere
and is now nearly double the rates from just three months ago. As seen from
south of the equator, meteor rates are still decent but falling rapidly. The
sporadic rates seen at the beginning of the month will be twice as much as
those seen during the last days of the month. The Perseid radiant does not
rise high into the sky as seen in the southern hemisphere so rates from this
shower are greatly reduced when compared to the northern hemisphere.

During this period the moon waxes from just past first quarter on the 9th to
a nearly full moon on the 15th. This week the moon will be located in the
evening sky as the sun sets and set during the morning hours. The window of
darkness between moon set and the start of morning twilight starts near six
hours and decreases to zero. Successful observations can be obtained while
the moon is up but much better results can be seen when the moon is low or
beneath the horizon. As seen from the mid-northern hemisphere (45 N) the
estimated total hourly rates during the evening observers would be near two.
For morning observers the estimated total hourly rates should be near
thirty. For those located in the mid-southern hemisphere (45 S) morning
rates would also be near twenty and evening rates near two. Locations
between these two extremes would see activity between the listed figures.
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. Moonlight reduces
meteor activity during the evening hours this week.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning August 9/10. 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 18:56
(284) +58. This position is located in southern Draco, five degrees
northwest of the fourth magnitude star Kappa Cygni. As seen from the
northern hemisphere, 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.

Alpha Capricornid (CAP) activity is nearly over for 2008. A few leftover
shower members may still be see from a wide radiant located at 21:12
(318) -06. This position lies in western Aquarius, four degrees west of the
third magnitude star Sadalsuud (Beta Aquarii). The radiant is best placed
near 0100 local daylight time (LDT), when it lies on the meridian and is
highest in the sky. Current rates would be less than one per hour no matter
your location. Don't confuse these meteors with the nearby 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, a bit slower than
the antihelions. This radiant is well seen except for far northern latitudes
where it remains twilight all night long and the radiant does not rise as
high into their sky.

The large Antihelion (ANT) radiant is now centered at 22:00 (330) -10. This
area of the sky lies on the Capricornus/Aquarius border, ten degrees south
of the third magnitude star Sadalmelik (Alpha Aquarii). Actually any meteor
from eastern Capricornus as well as western Aquarius, could be a candidate
for this shower. 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 for northern observers and three for observers 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 still active from a radiant at 23:16
(349) -13. This position lies in southern Aquarius, five degrees east of the
third magnitude star Delta Aquarii. The radiant is best placed near 0300
LDT, when it lies highest in the sky. Current rates would range from one to
two shower members per hour, depending on your latitude. 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.

The Perseids (PER) peak on Tuesday morning August 12 with average hourly
rates expected near one per minute. This weekend viewers in the northern
hemisphere should see 10-20 Perseids per hour during the dark morning hours
after the moon has set. The current radiant position lies at 03:00 (045)
+57, which is located in extreme northwestern Perseus, four degrees north of
the third magnitude star Gamma 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. More details on viewing the Perseid meteor shower are
available at: http://www.amsmeteors.org/showers.html#PER

As seen from the mid-northern hemisphere (45N) the Sporadic rates are
becoming more active. One would expect to see approximately twelve random
meteors during the last hour before dawn from rural observing sites and two
per hour during the evening hours. As seen from the mid-southern hemisphere
(45S) morning rates would be near ten per hour as seen from rural observing
sites and two per hour during the evening hours. Locations between these two
extremes would see activity between the listed figures. Moonlight reduces
sporadic activity during the evening hours this week.

The table below presents a summary of the expected activity this week. Rates
and positions are exact for Saturday night/Sunday morning but may be used
all week.

Kappa Cygnids (KCG)   18:56 (284) +58   Velocity - 25km/sec.
Northern Hemisphere Hourly Rates - 1   Southern Hemisphere Hourly Rates -<1

Alpha Capricornids (CAP)   21:12 (318) -06   Velocity - 23km/sec.
Northern Hemisphere Hourly Rates - <1   Southern Hemisphere Hourly Rates -<1

 Antihelion (ANT)  22:00 (330) -10   Velocity - 30km/sec.
Northern Hemisphere Hourly Rates - 2   Southern Hemisphere Hourly Rates - 3

Delta Aquariids (SDA)   23:16 (349) -13   Velocity 41km/sec.
Northern Hemisphere Hourly Rates - 1   Southern Hemisphere Hourly Rates - 2

 Perseid (PER)   03:00 (045) +57   Velocity - 59km/sec.
Northern Hemisphere Hourly Rates - 15   Southern Hemisphere Hourly Rates  -
5

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#X2008

Clear Skies!
Robert Lunsford
American Meteor Society