(meteorobs) Meteor Activity Outlook for July 18-24, 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 moon reaches its new phase on Wednesday July 22nd. At
this time it will lie near the sun and will be invisible at night. The
estimated total hourly rates for evening observers this week is near four 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 sixteen for those located in the mid-northern hemisphere (45 N) and
twenty two 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.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning July 18/19. 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 19:52
(298) -12. This position lies in extreme northeastern Sagittarius, five
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 near 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 20:36 (309) -17. This
area of the sky lies in western Capricornus, five degrees southeast of the
third magnitude star Beta Capricornii. Actually any meteor from Capricornus,
southeastern Aquila, southwestern Aquarius, 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
21:32 (323) -03, which is located three degrees north 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 Delta Aquariids (SDA) become active next week with rates of 1-2 per
hour. The radiant is located at 22:12 (333) -18. This position lies in
southwestern Aquarius, ten degrees west of the third magnitude star Delta
Aquarii. The radiant is best placed near 0300 LDT, when it lies highest in
the sky. The optimal latitudes for viewing this shower lie in the southern
tropics where the radiant passes overhead. With an entry velocity of 43
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 Pisces Austrinids (PAU) is a weak shower with a radiant is located at
22:16 (334) -33. This area of the sky lies in southern Piscis Austrinus,
twelve 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 one per hour from the
southern hemisphere and less than one 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.

The Perseids (PER) are now active from a radiant located at 00:40 (010) +52.
This position lies in southern Cassiopeia, five degrees south 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 to two 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 ten 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 fifteen 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.

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.

Alpha Capricornids  (CAP) - 19:52 (298) -12   Velocity - 24km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - 1

Antihelion (ANT) - 20:36 (309) -17   Velocity - 30km/sec.
Hourly Rates - Northern Hemisphere 2 - Southern Hemisphere - 3

North June Aquilids (NZC) - 21:32 (323) -03   Velocity - 40km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - <1

Delta Aquariids (SDA) - 22:12 (333) -18   Velocity - 43km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - 1

Pisces Austrinids (PAU) - 22:16 (334) -33   Velocity - 35km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - 1

Perseids  (PER) - 00:40 (010) +52   Velocity - 59km/sec.
Hourly Rates - Northern Hemisphere 2 - 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