Meteor Activity Outlook for July 12-18, 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.