Meteor Activity Outlook for May 16-22, 2009

May is a fairly slow month for meteor activity.
The Eta Aquariids are very active the first two weeks of the month then fade as
the month progresses. The only other showers active this month are the Eta Lyrids
and the Antihelion radiant. These will add only 1-2 meteors per hour to the total
count. Sporadic rates are low but steady as seen from the mid-northern hemisphere
(45 N). Sporadic rates seen from the mid-southern hemisphere (45 S) continue
to rise this month toward a maximum in July.

During this period the moon reaches it last quarter
phase on Sunday May 17. On this date the half illuminated moon will rise near 0100
local daylight time (LDT)and will remain in the sky the during the remainder of the
night. Later in the period the waning crescent moon will rise later in the morning
offering more dark skies. The estimated total hourly rates for evening observers this week is near
one as seen from the northern hemisphere and two for those situated south of the
equator. For morning observers the estimated total hourly rates should be near
six for those located in the mid-northern hemisphere (45 N) and fourteen for those
viewing from the mid-southern hemisphere (45 S). 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. Morning rates are reduced due to moonlight.

The radiant positions and rates listed below are exact
for Saturday night/Sunday morning May 16/17. 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 wide Antihelion (ANT) radiant is now centered at 16:36 (249) -22. This
area of the sky lies in extreme southeastern Ophiuchus, five degrees northeast of
the first magnitude orange star Antares (Alpha Scorpii). This radiant is best placed
near 0200 LDT when it is located on the meridian and lies highest in the sky above
the horizon. Due to the large size of this radiant, any meteor radiating from
southern Ophiuchus or northern Scorpius could be a candidate for this shower. Rates
at this time should be near two per hour as seen from the southern hemisphere and
only one as seen from north of the equator. With an entry velocity of 30km/sec.,
the average Antihelion meteor would be of medium-slow speed.

The Eta Aquariids (ETA) are now dwindling in numbers. 1-2 may be seen in
the hour before dawn from tropical locations. The radiant is currently located
at 23:08 (347) +04. This area of the sky is located in extreme western Pisces,
three degrees northwest of the fourth magnitude star Gamma Piscium. The best time
to view this activity is during the hour before the start of morning twilight,
when the radiant lies highest in a dark sky. With an entry velocity of 68 kilometers
per second, a majority of these meteors will appear to move swiftly.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately
four Sporadic meteors per hour during the last hour before dawn as seen
from rural observing sites. Evening rates would be near one per hour. As seen from
the mid-southern hemisphere (45S), morning rates would be near ten 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. Morning
rates are reduced due to moonlight.

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.