(meteorobs) Meteor Activity Outlook for July 12-18, 2008

Robert Lunsford lunro.imo.usa at cox.net
Fri Jul 11 18:04:28 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 full phase on Friday July 18th. At
that time the moon will be located 180 degrees from of the sun and will be
in the sky all night long. This weekend successful observations may be
obtained between the time of moonset and dawn. The window of darkness
shrinks until July 17, when it essentialy reached zero. As seen from the
mid-northern hemisphere (45 N) the estimated total hourly rates during the
evening observers would be near two. For morning observers the estimated
total hourly rates should be near twelve. For those located in the
mid-southern hemisphere (45 S) morning rates would be near twenty 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. Evening rates are reduced due to moonlight.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning July 12/13. 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 19:28
(292) -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 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
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 20:12 (303) -18. This
area of the sky lies in western Capricornus, three 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.

Sirko Molau's study of video radiants has revealed activity during the
period July 8-22, from an area in northwestern Aquarius. The first of two
maximums occured on July 10 with the radiant located at 21:00 (315) -04.
This position lies five degrees northwest of the third magnitude star
Sadalsuud (Beta Aquarii). This radiant is best placed near 0300 LDT when it
lies highest in the sky. Rates would most likely be less than one shower
member per hour no matter your location. At 40km/sec., the average meteor
from this radiant would be of medium velocity.

The Delta Aquariids (SDA) are active from a radiant located at 21:48
(327) -19. This position lies in eastern Capricornus, two degrees south of
the third magnitude star Nashira (delta Capricornii). The radiant is best
placed near 0300 local daylight time, when it lies highest in the sky.
Current rates would be low, less than one shower member per hour. 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. This shower peaks on July 27th
with expected ZHR's near twenty.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are
finally beginning to increase. One would expect to see approximately nine
random meteors during the last hour before dawn from rural observing sites
and two per hour during the evening hours. As seen from the mid-southern
hemisphere (45S) morning rates would be near seventeen 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.
Evening rates are reduced due to moonlight.

The table below presents a condensed version of the expected activity this
week. Rates and positions are exact for Saturday night/Sunday morning.

Alpha Capricornids (CAP)  19:28 (292) -14    Velocity - 23km/sec.
Northern Hemisphere - <1   Southern Hemisphere - <1

Antihelion (ANT) - 20:12 (303) -18   Velocity - 30km/sec.
Northern Hemisphere - 2   Southern Hemisphere - 3

Beta Aquariids (BAQ)  21:00 (315) -04   Velocity - 40km/sec.
Northern Hemisphere - <1   Southern Hemisphere - <1

Delta Aquariids (SDA)  21:48 (327) -19   Velocity - 41km/sec.
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#X2008

Clear Skies!
Robert Lunsford
American Meteor Society





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