(meteorobs) Meteor Activity Outlook for July 11-17, 2009

[Robert Lunsford]

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 list 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.

Alpha Capricornids  (CAP) - 19:24 (291) -14   Velocity - 24km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - 1

Antihelion (ANT) - 20:08 (302) -19   Velocity - 30km/sec.
Hourly Rates - Northern Hemisphere 2 - Southern Hemisphere - 3

North June Aquilid (NZC) - 21:04 (316) -04   Velocity - 40km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - <1

Perseids  (PER) - 00:04 (001) +49   Velocity - 59km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - <1

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#X2009

Clear Skies!
Robert Lunsford
American Meteor Society