(meteorobs) Meteor Activity Outlook for July 25-31, 2009

Robert Lunsford lunro.imo.usa at cox.net
Fri Jul 24 14:35:45 EDT 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.

Alpha Capricornids  (CAP) - 20:16 (304) -11   Velocity - 24km/sec.
Hourly Rates - Northern Hemisphere 2 - Southern Hemisphere - 2

Antihelion (ANT) - 21:04 (316) -15   Velocity - 30km/sec.
Hourly Rates - Northern Hemisphere 2 - Southern Hemisphere - 3

Delta Aquariids (SDA) - 22:28 (337) -17   Velocity - 43km/sec.
Hourly Rates - Northern Hemisphere 5 - Southern Hemisphere - 7

Pisces Austrinids (PAU) - 22:36 (339) -31   Velocity - 35km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - 2

Perseids  (PER) - 01:32 (023) +53   Velocity - 59km/sec.
Hourly Rates - Northern Hemisphere 3 - 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




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