Meteor Activity Outlook for August 1-7, 2009

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 21:24 (321) -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 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.