Meteor Activity Outlook for July 25-31, 2009

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 first
quarter phase on Tuesday July 28th. At this time the moon will be located ninety
degrees east of the sun and will set near 0100 local daylight time (LDT). This
weekend the waxing crescent moon will set long before the prime morning observing
hours arrive. 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 four for those located in the mid-northern hemisphere
(45 N) and twenty eight 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 July 25/26. 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
20:16 (304) -11. This position lies in extreme northwestern Capricornus, just two
degrees north of the third magnitude double star Alpha Capricornii. The radiant is
best placed near 0100 (LDT), when it lies on the meridian and is highest in the
sky. With maximum activity occurring on the 28th, current rates would be near two
per hour, no matter your location. 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
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 21:04 (316) -15.
This area of the sky lies in central Capricornus, two degrees north of the
fourth magnitude start Theta Capricornii. Actually any meteor from Capricornus,
southeastern Aquila, 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 the 30th with ZHR’s
near twenty. You will not see twenty per hour unless you are watching from dark
tropical areas where the radiant approaches the zenith. More likely, you will see
ten shower members per hour, depending on your latitude and the hour of the night.
The radiant is located at 22:28 (337) -17. This position lies in southwestern
Aquarius, seven degrees west of the third magnitude star Delta Aquarii. The radiant
is best placed near 0300 LDT, when it lies highest in the sky. With an entry
velocity of 43 km/sec., most activity from this radiant would be of average speed.
These meteors tend to be faint so the darkest skies are necessary in order to see
this shower well.

The Pisces Austrinids (PAU) is a weak shower with a radiant is located at
22:36 (339) -31. This area of the sky lies in central Piscis Austrinus, eight
degrees southwest 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 two per hour from the southern hemisphere and
one from the north. At 35/km per second, these meteors are of average velocity,
slower than the Delta Aquariids but faster than the Alpha Caps and the antihelion
meteors.

The Perseids (PER) are now active from a radiant located at 01:32 (023)
+53. This position lies on the Cassiopeia/Perseus border, four degrees southeast
of the fourth magnitude star Theta Cassiopeiae. The radiant is best placed during
the last hour before the start of morning twilight when it lies highest in a dark
sky. Current rates would be near three per hour, as seen from the northern
hemisphere. Activity from this source is not visible south of 40 degrees south
latitude. With an entry velocity of 59 km/sec., most activity from this
radiant would be swift.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately
eleven Sporadic meteors per hour during the last hour before dawn as seen
from rural observing sites. Evening rates would be near three per hour. As seen from
the mid-southern hemisphere (45S), morning rates would be near thirteen 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. Evening
rates are reduced by 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.