(meteorobs) Meteor Activity Outlook for May 18-24, 2007

[Robert Lunsford]

May provides the peak of the Eta Aquarid meteor shower. This is the
strongest shower visible from the southern hemisphere but unfortunately this
year glare from the waning gibbous moon will obscure all but the brightest
meteors. The much weaker Eta Lyrids peak on May 9 under slightly better
conditions. Sporadic rates seen in the northern hemisphere are nearing the
nadir of their activity curve. The lowest rates are observed in June. On a
positive note, rates seen from the southern hemisphere are increasing toward
a July maximum.

During this period the moon reaches its first quarter phase on Wednesday May
23. At this time the moon will set near 0100 local daylight time and will
not interfere with prime time morning observing. This weekend the waxing
crescent moon will set during the early evening hours and will not interfere
with the more productive morning hours. The estimated total hourly rates for
evening observers this week is near two for those north of the equator and
three for observers south of the equator. For morning observers the
estimated total hourly rates should be near seven for those located in the
northern hemisphere and eighteen 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 May 19/20. 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 Antihelion (ANT) radiant is now centered at 16:48 (252) -22. This area
of the sky is centered in southwestern Ophiuchus, five degrees northeast of
the orange first magnitude star Antares (Alpha Scorpii). 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 one 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.

The Eta Aquarids (ETA) are particles from Halley's Comet, which last passed
through the inner solar system in 1986. The Earth's orbit does not currently
pass through recent orbits of Halley's comet. Rather, the meteors we now see
as Eta Aquarids were produced by the comet many hundreds of years ago when
the orbit of the comet was located much closer to the Earth. The maximum of
the Eta Aquarids occurred on May 6. At that time rates can reach thirty
shower members per hour as seen from the northern tropical areas southward.
Current rates would vary from zero to two per hour depending on your
latitude and observing conditions. The radiant is located at 23:16 (349)
+05. This area of the sky is located in western Pisces near the fourth
magnitude star Gamma Piscium. The best time to view this activity is just
before the start of morning twilight, when the radiant lies highest in a
dark sky. With an entry velocity of 66 kilometers per second, a majority of
these meteors will appear to move swiftly.

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

Antihelion (ANT) - 16:48 (252) -22
Northern Hemisphere - 1   Southern Hemisphere - 3

Eta Aquarids (ETA)  23:16 (349) +05
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#X2007

Clear Skies!
Robert Lunsford
American Meteor Society