(meteorobs) Meteor Activity Outlook for July 13-19, 2007

[Robert Lunsford]

For observers in the northern hemisphere meteor activity finally picks up in
July after months of low rates. Several showers become active this month and
peak toward the end of the month. Sporadic activity increases with each
passing week throughout the northern summer. Activity seen in the southern
hemisphere is peaking and will remain strong throughout the month. Later in
the month strong minor shower activity will offset the falling sporadic
rates in the south. Sporadic rates as seen from the southern hemisphere are
highest early in the month and then fall quite steeply as the southern
winter progresses.

During this period the moon reaches its new phase on Saturday July 14. At
this time the moon is located near the sun as seen in the sky and not
visible at night. Later in the period the thin waxing crescent moon will
enter the evening sky but will set well before the prime morning observing
hours. The estimated total hourly rates for evening observers this week is
near three for those located north of the equator and four for observers
south of the equator. For morning observers the estimated total hourly rates
should be near fifteen for those located in the northern hemisphere and
twenty for those viewing from south of the equator. 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 listed below are exact for Saturday night/Sunday
morning July 14/15. 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. Doing this 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 19:36
(294) -14. This position lies in northeastern Sagittarius, seven degrees
southwest of the third magnitude star Alpha Capricornii. The radiant is best
placed near 0100 local daylight time, when it lies highest in the sky.
Current rates would be near one per hour, no matter your location. Don't mix
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. 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 Antihelion (ANT) radiant is now centered at 20:20 (305) -18. This area
of the sky is located in a western Capricornus, four degrees south of the
third magnitude star Dabih (Beta Capricornii). 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 per hour as seen in the northern hemisphere
and three per hour for those located 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 8-15, from an area in northwestern Aquarius. Maximum 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. It
appears that nine percent of the total sporadic activity for the night is
related to this radiant. This would equate to only 1-2 shower members per
hour at best. At 40km/sec., the average meteor from this radiant would be of
medium velocity.

Sirko Molau's study of video radiants has revealed another center of
activity located at 21:32 (323) -02. This radiant is active during the
period July 18-23, from an area in northern Aquarius. This position lies
four degrees southwest of the third magnitude star Sadalmelik (Alpha
Aquarii). Maximum occurs on July 20. This radiant is best placed near 0300
LDT when it lies highest in the sky. It appears that seven percent of the
total sporadic activity for the night is related to this radiant. This would
only provide 1-2 shower members per hour at best. At 39km/sec., the average
meteor from this radiant would be of medium velocity.

The Delta Aquariids (SDA) are active from a radiant located at 21:56
(329) -19. This position lies in eastern Capricornus, four degrees southeast
of the variable star Epsilon Capricornii. The radiant is best placed near
0400 local daylight time, when it lies highest in the sky. Current rates
would be low perhaps two per hour visible from the southern hemisphere and
one per hour from the northern hemisphere. 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 28 with expected ZHR's
near twenty.

Sirko Molau's study of video radiants has revealed early Perseid activity
peaking on July 20. The radiant is then located at 00:48 (012) +51, which
places it southern Cassiopeia, six degrees south of the second magnitude
star Shedar (Alpha Cassiopeiae). This radiant is best placed at dawn when it
lies highest in the sky. This enhancement of Perseid meteors is active July
15-22 when rates may rise to 2-3 per hour. At 52km/sec., the average meteor
from this radiant would be of medium-swift velocity with a good percentage
of trains.

Sporadic rates are now rising for observers in the northern hemisphere and
are peaking for those located south of the equator. One would expect to see
perhaps ten random meteors during the last hour before dawn from rural
observing sites located in the northern hemisphere. During the first dark
hour after the end of evening twilight, perhaps three random meteors can be
seen per hour. Sporadic rates increase as the night progresses so rates seen
near midnight would be near six per hour. Late morning sporadic rates seen
from the southern hemisphere are now near sixteen per hour from rural
observing sites. During the first dark hour after the end of evening
twilight, perhaps four random meteors can be seen per hour, increasing to
eight by midnight.

Alpha Capricornid (CAP)  19:36 (294) -14
Northern Hemisphere -1   Southern Hemisphere - 1

Antihelion (ANT) - 19:52 (298) -19
Northern Hemisphere -1   Southern Hemisphere - 2

Beta Aquarids (BAQ)  21:00 (315) -04
Northern Hemisphere ->1   Southern Hemisphere - >1

Alpha Aquarids (AAQ)  20 21:32 (323) -02
Northern Hemisphere ->1   Southern Hemisphere - >1

Delta Aquariids (SDA)  21:56 (329) -19
Northern Hemisphere -1   Southern Hemisphere - 1

Perseids (PER)  00:48 (012) +51 52 07:00 2 - >1 I
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#X2007

Clear Skies!
Robert Lunsford
American Meteor Society