(meteorobs) Meteor Activity Outlook for August 30-September 5, 2008

[Robert Lunsford]

September offers longer nights and cooler temperatures in the northern
hemisphere. In the sky, no major showers are visible from either hemisphere
but the northern hemisphere enjoys the advantage of higher sporadic rates.
The two recognized minor showers active in early September have high
northern declinations (celestial latitude) therefore are much better suited
to be viewed from locations north of the equator. Toward the end of the
month the antihelion radiant becomes entangled with the two Taurid radiants
and it is impossible to separate them. Therefore the antihelion radiant will
be excluded from the list from the last week of September until the end of
the Taurid activity period late in November. Observers in the southern
hemisphere suffer from some of their lowest rates of the year this month.
The Taurid radiants are not too badly placed so observers south of the
equator can expect to see a little of this activity toward the end of the
month.

During this period the moon reaches its new phase on Saturday August 30. At
this time the moon will rise and set with the sun and will not be visible at
night. As the week progresses the waxing crescent moon will enter the
evening sky but will set during the early evening hours allowing observers
to view in dark skies the remainder of the night. The estimated total hourly
rates for evening observers this week is near three for those located in the
mid-northern hemisphere (45 N) and two for those viewing from the
mid-southern hemisphere (45 S). For morning observers the estimated total
hourly rates should be near eighteen for those located in the mid-northern
hemisphere (45 N) and ten for those viewing from the mid-southern hemisphere
(45 S). 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 and rates listed below are exact for Saturday
night/Sunday morning August 30/31. 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:

Sirko Molau's study of video radiants has shown an active radiant located in
Ursa Minor during this period. The September Ursid Minorids (SUM) peak on
September 1st with a radiant located near 17:24 (261) +83. The area of the
sky is located in central Ursa Minor not far from Polaris, the North Star.
This radiant is circumpolar for areas north of 7 degrees north latitude.
Interestingly enough, just 14 degrees further south at 7 degrees south
latitude, it cannot be seen at all! It reaches its highest altitude above
the horizon near 1900 (7pm) LDT. Most locations in the northern hemisphere
are not dark until an hour or two later so the period just as dusk settles
in would be the best time to try and observe this activity. Hourly rates
would most likely be less than one. With an entry velocity of 38 km/sec.,
most members of the September Ursid Minorids would possess a medium
velocity.

Another entry in Sirko Molau's study of video radiants is located in Draco
during this period. The August Draconid (AUD) radiant lies near 19:28 (292)
+65, which is half-way between the bright stars Kochab (Beta Ursae Minoris
and Deneb (Alpha Cygni). This radiant is circumpolar for locations north of
25 degrees north latitude. It reaches its highest altitude above the horizon
near 2200 LDT, therefore is best seen during the evening hours. Maximum
activity occurred on August 27. Hourly rates this weekend would most likely
be less than one. The northern hemisphere is heavily favored for viewing
this activity. With an entry velocity of 30 km/sec., most members of the
August Draconids would possess a medium-slow velocity. It should be noted
that if the Kappa Cygnid period is extended past August 25, the radiant
drift would be similar to the August Draconids.

The large Antihelion (ANT) radiant is now centered at 23:20 (350) -03. This
area of the sky lies on the Pisces/Aquarius border, three degrees northeast
of the fourth magnitude Phi Aquarii. Actually, the radiant is so large that
any meteor from northeastern Aquarius, western Pisces, or southwestern
Pegasus 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. Hourly
rates at this time should be near three no matter your location. With an
entry velocity of 30 km/sec., the average Antihelion meteor would be of
medium-slow speed.

The Aurigids (AUR) reach maximum activity on the morning of August 31st. The
radiant is located near 05:36 (084) +42. This position is located in central
Auriga, four degrees southeast of the brilliant zero magnitude yellow star
Capella (Alpha Aurigae). This radiant is circumpolar north of 48 degrees
north latitude. For areas further south in the northern hemisphere, the
radiant rises during the late evening hours. From south of the equator the
radiant will rise during the late morning hours (if at all) depending on
your southern latitude. Regardless of location the radiant is best placed
during the last dark hour before morning twilight when it lies highest in
the sky. Hourly rates on Monday morning are expected to be near five. Unlike
last year, no outburst is expected from this shower. At 66 km/sec., these
meteors are swift, often exhibiting persistent trains.

The Southern September Lyncid (SSL) is another shower discovered by Sirko
Molau in his study of video radiants. This shower is active from August 28th
through September 5th and peaks on the morning of September 1st. The radiant
actually lies in extreme eastern Auriga, just over the border from Lynx.
This position also lies six degrees north of the famous double star Castor
(Alpha Geminorum). The radiant rises near 0100 LDT and reaches its highest
altitude above the horizon near 0900 LDT. Since this is during daylight
hours the best time to view activity from the Southern September Lyncids
would be during the last dark hour before dawn. The much stronger Aurigids
are active the same night and care must be taken to avoid confusing the two
showers. Both showers produce swift meteors but the Aurigids would be far
more numerous. If any observer is serious about seeing any of this activity
they should include both radiants within their field of view. Viewing toward
the north would also allow the monitoring of the September Ursa Minorids.
With an entry velocity of 52km/sec., most members of the Southern September
Lyncids would move swiftly

As seen from the mid-northern hemisphere (45N) one would expect to see
approximately thirteen 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 six per hour as seen from rural observing sites and two per
hour during the evening hours. Locations between these two extremes would
see activity between the listed figures.

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.

September Ursid Minorids (SUM)   17:24 (261) +83   Velocity - 38km/sec.
Northern Hemisphere - <1   Southern Hemisphere - <1

 August Draconids (AUD)   19:28 (292) +65   Velocity - 30km/sec.
Northern Hemisphere - <1   Southern Hemisphere - <1

Antihelion (ANT)   23:20 (350) -03   Velocity - 30km/sec.
Northern Hemisphere - 3   Southern Hemisphere - 3

 Aurigids (AUR)   05:36 (084) +42   Velocity - 66km/sec.
Northern Hemisphere - 2   Southern Hemisphere - <1

Southern September Lyncid (SSL)   07:24 (111) +39   Velocity - 52km/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