The moon is a major factor in observing plans this week. It
is currently more than 75 percent illuminated and getting brighter
day by day. The Perseid
meteor shower is the major event for this week and of the
summer. The moon will set an hour or two (depending on your latitude)
before morning twilight on Saturday August 12, the peak morning.
The hour before dawn on Sunday would also provide good rates.
Beyond that the moon will be in the sky all night spoiling the
chances of seeing the high activity usually seen this month.
Now is the time to watch for the Perseids. Rates seen in moon
less skies are now between 5-10 per hour and climbing steadily.
Normally a few Perseids can be seen during the evening hours but
with the bright moon these would be few and far between. I would
advise waiting until the moon is 10-15 degrees above the horizon.
An hour before the time of moon set would be a good starting point.
At this altitude the atmosphere will begin to dim the moon allowing
more activity to be seen. It is often dramatic to see the darkness
increase as the moon approaches the horizon as if a heavenly dimmer
switch has been turned down. If watching from a rural site the
Milky Way will suddenly be visible along with many hundreds of
dim stars not seen before. Since many Perseids meteors are dim,
more and more activity will also appear.
On the 12th, the Perseid radiant will be located at 03:04 (046)
+58 (What does
this mean?), which is in the extreme northwest portion of
the constellation of Perseus near the famous "Double
Cluster". This area of the sky does not set for observers
north of latitude 42 degrees. Even from high northern latitudes
the radiant is low in
the northern sky until late in the evening. I would advise observers
to face anywhere from due north to due east especially if the
moon is still above the horizon. Once the moon has set Perseid
meteors can be seen in any part of the sky. If the radiant is
high in the sky, as it will be after moon set, I always look in
a direction so that the radiant is included in my field of view.
This way I can see meteors shootng in all directions including
straight down. Facing the northeast quadrant of the sky will include
the Perseid radiant all morning long.
Once the moon has set I would expect observers to see 25-50 Perseids
per hour depending on their level of local light pollution. The
Perseid meteors are also rich in fireballs
and persistent trains. Due to their high numbers they are also
photogenic with an average of 1 to 2 meteors captured on each
roll of 24 exposure (15 minutes each) ISO 400 using a standard
50 mm lens.
There are other sources of activity this week. The following list
gives the positions and the expected rates per hour on Saturday
morning August 12.