Meteor Activity Outlook for May 21-27, 2011

During this period the moon reaches its last quarter phase on Tuesday May 24th.
At this time the moon will lie ninety degrees west of the sun and will rise near
0100 local daylight time (LDT) for observers at mid-northern latitudes. This
weekend the waning gibbous moon will seriously interfere with meteor observing
as the fainter meteors will be obscured by the lunar glare. As the week
progresses conditions will improve and the moon wanes and rises later in the
morning. The estimated total hourly rates for evening observers this week is
near three as seen from the northern hemisphere and four as seen from the
southern hemisphere. For morning observers the estimated total hourly rates
should be near four from the northern hemisphere and nine as seen from south of
the equator. 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. Morning rates are reduced due to moonlight.

The radiant (the area of the sky where meteors appear
to shoot from) positions and rates listed below are exact for Saturday night/Sunday
morning May 21/22. 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 shower is expected to be active this week:

The wide Antihelion (ANT) radiant is now centered at 16:56 (254) -22. This area
of the sky lies in southwestern Ophiuchus, six degrees northeast of the first
magnitude orange star Antares (Alpha Scorpii). This radiant is best placed near
0200 LDT when it lies on the meridian and is located highest in the sky. Due to
the large size of this radiant, any meteor radiating from eastern Libra,
northern Lupus, southern Ophiuchus, southern Sagittarius, or Scorpius could be a
candidate for this shower. Rates at this time should be near one per hour as
seen from the northern hemisphere and two per hour as seen from south of the
equator. With an entry velocity of 30 km/sec., the average Antihelion meteor
would be of medium-slow speed.

AAs seen from the mid-northern hemisphere (45N) one would expect to see
approximately three sporadic meteors per hour during the last hour before dawn
as seen from rural observing sites. Evening rates would be near two per hour. As
seen from the mid-southern hemisphere (45S), morning rates would be near seven
per hour as seen from rural observing sites and three per hour during the
evening hours. Locations between these two extremes would see activity between
the listed figures. Morning 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.