(meteorobs) Meteor Activity Outlook for August 1-7, 2009

[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. This 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 reaches its full phase on Thursday August 6th.
This weekend and early next week there is a window of opportunity to view
the meteor activity during the dark period between moonset and dawn. This is
especially true for observers viewing from the northern hemisphere as the
moon currently lies well south of the ecliptic. As Wednesday arrives the 
full
moon is in the sky nearly the entire night. The estimated total hourly rates
for evening observers this week is near four no matter your location. For
morning observers the estimated total hourly rates should be near twenty
seven for those located in the mid-northern hemisphere (45 N) and twenty
five for those viewing from the mid-southern hemisphere (45 S). 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. Evening rates are
reduced due to moonlight.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning August 1/2. 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 18:52
(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 20:40
(310) -8. This position lies in western Aquarius, three degrees northwest of
the fourth magnitude star Epsilon 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 near two 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 24
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 21:28 (322) -13. This
area of the sky lies in northeastern Capricornus, five degrees northwest of
the third magnitude star Delta Capricornii. 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 active from a radiant at 22:48 (342) -15. This
position lies in southwestern Aquarius, very close to the third magnitude
star Delta Aquarii. The radiant is best placed near 0300 LDT, when it lies
highest in the sky. Current rates would be lie between five and ten shower
members per hour, depending on your latitude. With an entry velocity of 43
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 Piscis Austrinids (PAU) is a weak shower with a radiant is located at
23:00 (345) -28. This area of the sky lies in western Piscis Austrinus, just
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 Aquariids 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 gradually as we approach the peak on
the morning of August 12. The current radiant position lies at 02:12 (033)
+55, which is located in extreme northwestern Perseus, just three degrees
south of the famous "Double Cluster". The nearest easily seen star is Eta
Persei which lies six degrees to the northeast. 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 witnessed 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.

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 eleven 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. Evening
rates reduced due to moonlight.

The list 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) 18:52 (283) +58 Velocity - 25km/sec.
Northern Hemisphere - 1 per hr. Southern Hemisphere - <1 per hr.

Alpha Capricornids (CAP) 20:40 (310) -08 Velocity - 23km/sec.
Northern Hemisphere - 1 per hr. Southern Hemisphere - 2 per hr.

Antihelion (ANT) - 21:24 (321) -13 Velocity - 30km/sec.
Northern Hemisphere - 2 per hr. Southern Hemisphere - 3 per hr.

Delta Aquariids (SDA) 22:48 (342) -15 Velocity - 41km/sec.
Northern Hemisphere - 2 per hr. Southern Hemisphere - 5 per hr.

Pisces Austrinids (PAU) 23:00 (345) -28 Velocity - 35km/sec.
Northern Hemisphere - <1 per hr. Southern Hemisphere - 1 per hr.

Perseid (PER) 02:12 (033) +55 Velocity - 59km/sec.
Northern Hemisphere - 5 per hr. Southern Hemisphere - 1 per hr.

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#X2009

Clear Skies!
Robert Lunsford
American Meteor Society