Meteor Activity Outlook for July 26-August 1, 2008

After several months of low activity the meteor
rates for both hemispheres see a marked increase in July. In the northern hemisphere
the change is not noticeable until mid-month when several southern radiants, the
Perseids, and sporadic rates all increase in activity. Southern rates are good all month long.

During this period the moon reaches its new
phase on Friday August 1st. At that time the moon will be located near the sun
and will not be visible in the night sky. This weekend the waning crescent moon
will light the morning skies but successful observations may still be obtained by
facing in a direction so that the moon is out of your field of view. As seen from the
mid-northern hemisphere (45 N) the estimated total hourly rates during the evening
observers would be near three. For morning observers the estimated total hourly rates
should be near twenty five. For those located in the mid-southern hemisphere (45 S) morning
rates would be near thirty and evening rates near three. 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. Morning
rates are reduced due to moonlight.

The radiant positions and rates listed below are exact
for Saturday night/Sunday morning July 26/27. 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 Alpha Capricornids (CAP) are active from a wide radiant
located at 20:20 (305) -11. This position lies in northwestern Capricornus, two
degrees north of the third magnitude double star Alpha Capricornii. 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 for
those in the northern hemisphere and three as seen from the southern hemisphere.
Don’t confuse these meteors with the 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 21:08 (317) -15.
This area of the sky lies in northern Capricornus, two degrees north of the
third magnitude star Theta Capricornii. Actually any meteor from 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) reach maximum activity on Sunday July 27th from
a radiant located at 22:36 (339) -16. This position lies in southwestern Aquarius,
three degrees west 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 ten to fifteen shower members per hour, depending on your latitude. The
optimal latitudes for viewing this shower lie in the southern tropics where the
radiant passes overhead. 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 moon may affect
rates more than usual for this shower.

The Pisces Austrinids (PAU) is a weak shower with a radiant is located at
22:44 (341) -30. This area of the sky lies in western Piscis Austrinus, five
degrees west 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 three per hour from the southern hemisphere and near two
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 three 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 01:40 (025) +53,
which is located in extreme northwestern Perseus. The nearest easily seen star is
fourth magnitude 51 Andromedae, lying five degrees to the south of the Perseid
radiant. 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.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are
finally beginning to increase. One would expect to see approximately eight
random meteors during the last hour before dawn from rural observing sites and
three per hour during the evening hours. As seen from the mid-southern hemisphere
(45S) morning rates would be near nine per hour as seen from rural observing
sites and three per hour during the evening hours. Locations between these two
extremes would see activity between the listed figures. Morning rates are 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.