Meteor Activity Outlook for July 11-17, 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 waning moon still compromises
observing attempts, especially during the morning hours. Conditions improve with
each passing night as the moon rises later and later. The estimated total
hourly rates for evening observers this week is near three as seen from the northern
hemisphere and five for those situated south of the equator. For morning observers
the estimated total hourly rates should be near ten for those located in the
mid-northern hemisphere (45 N) and fourteen 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. Morning rates are reduced due to
moonlight.

The radiant positions and rates listed below are exact
for Saturday night/Sunday morning July 11/12. 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
19:24 (291) -14. This position lies in northeastern Sagittarius, a dozen degrees
west 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 less than one per hour, no matter
your location. Don’t confuse these meteors with the more numerous 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 20:08 (302) -19. This
area of the sky lies in western Capricornus, four degrees southwest of the
third magnitude star Beta Capricornii. Actually any meteor from western
Capricornus, southwestern Aquila, as well as eastern Sagittarius 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.

Studies by Sirko Molau of the IMO’s video data has revealed an active radiant
located in western Aquarius this time of year. The radiant lies at 21:04 (316)
-04, which is located six degrees southwest of the third magnitude star Sadalsuud
(Beta Aquarii). This radiant is best placed near 0300 LDT when it lies on the
meridian and is highest in the sky. Rates are most likely less than one per hour
regardless of your location. Maximum activity occurred on July 6th. With an entry
velocity of 40 km/sec., the average North June Aquilid (NZC) meteor would
be of medium speed, but noticeably more swift than the nearby Antihelion radiant.

The first Perseids (PER) begin to appear next week from a radiant located
at 00:04 (001) +49. This position lies in southern Cassiopeia, seven degrees
southwest of the second magnitude star Shedar (Alpha 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 less than one per hour, no matter
your location. 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
six Sporadic meteors per hour during the last hour before dawn as seen
from rural observing sites. Evening rates would be near two per hour. As seen from
the mid-southern hemisphere (45S), morning rates would be near ten per hour as
seen from rural observing sites and four per hour during the evening hours. Locations
between these two extremes would see activity between the listed figures. Morning
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.