(meteorobs) Meteor Activity Outlook for July 26-August 1, 2008

Robert Lunsford lunro.imo.usa at cox.net
Sat Jul 26 19:46:28 EDT 2008


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 Friday August 1st. At
that time the moon will be located near the sun and will not be visible in
the night sky. This weekend the waning crescent moon will light the morning
skies but successful observations may still be obtained by facing in a
direction so that the moon is out of your field of view. As seen from the
mid-northern hemisphere (45 N) the estimated total hourly rates during the
evening observers would be near three. For morning observers the estimated
total hourly rates should be near twenty five. For those located in the
mid-southern hemisphere (45 S) morning rates would be near thirty and
evening rates near three. 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 26/27. 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 20:20
(305) -11. This position lies in northwestern Capricornus, two degrees north
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 two per hour for those in
the northern hemisphere and three as seen from the southern hemisphere.
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 23 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 21:08 (317) -15. This
area of the sky lies in northern Capricornus, two degrees north of the third
magnitude star Theta Capricornii. Actually any meteor from Capricornus 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 Sunday July 27th from a
radiant located at 22:36 (339) -16. This position lies in southwestern
Aquarius, three degrees west of the third magnitude star Delta Aquarii. The
radiant is best placed near 0300 LDT, when it lies highest in the sky.
Current rates would range from ten to fifteen shower members per hour,
depending on your latitude. The optimal latitudes for viewing this shower
lie in the southern tropics where the radiant passes overhead. With an entry
velocity of 41 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 moon may affect rates more
than usual for this shower.

The Pisces Austrinids (PAU) is a weak shower with a radiant is located at
22:44 (341) -30. This area of the sky lies in western Piscis Austrinus, five
degrees west 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 three per hour from the southern
hemisphere and near two 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.

Perseid (PER) activity is now near three per hour as seen from the northern
hemisphere. These rates will increase gradually as we approach the peak on
the morning of August 12. The current radiant position lies at 01:40 (025)
+53, which is located in extreme northwestern Perseus. The nearest easily
seen star is fourth magnitude 51 Andromedae, lying five degrees to the south
of the Perseid radiant. The radiant is well placed for those in the Northern
Hemisphere during the last few hours before dawn. Due to the high northern
declination (celestial latitude) of the radiant, rates seen from the
Southern Hemisphere are very low when compared to those seen north of the
equator. At 59 km/sec., Perseid meteors are swift, often exhibiting
persistent trains.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are
finally beginning to increase. One would expect to see approximately eight
random meteors during the last hour before dawn from rural observing sites
and three per hour during the evening hours. As seen from the mid-southern
hemisphere (45S) morning rates would be near nine 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.
Morning rates are reduced due to 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)  20:20 (305) -11   Velocity - 23km/sec.
Northern Hemisphere - 2   Southern Hemisphere - 3

Antihelion (ANT) - 20:20 (305) -11   Velocity - 30km/sec.
Northern Hemisphere - 2   Southern Hemisphere - 3
 02:00 2 - 3 II

Delta Aquariids (SDA)  21:48 (327) -19   Velocity - 41km/sec.
Northern Hemisphere - 10  Southern Hemisphere - 15

Pisces Austrinids (PAU)  22:44 (341) -30   Velocity - 35km/sec.
Northern Hemisphere - 2   Southern Hemisphere - 3

Perseid (PER)  01:40 (025) +53   Velocity - 59km/sec.
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#X2008

Clear Skies!
Robert Lunsford
American Meteor Society




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