Meteor Activity Outlook for May 7-13, 2011

During this period the moon reaches its first quarter phase on Tuesday May 10.
At this time the moon will lie ninety degrees east of the sun and will set near
0100 local daylight time (LDT) for observers at mid-northern latitudes. 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 eighteen
from the northern hemisphere and thirty five 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. Evening rates are slightly 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 7/8. 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 16:00 (240) -21. This area
of the sky lies in western Scorpius, two degrees north of the second magnitude
star Dschubba (Delta 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 extreme eastern Hydra, Libra, northern
Lupus, southern Ophiuchus, or Scorpius could be a candidate for this shower.
Rates at this time should be near two per hour as seen from the northern
hemisphere and three 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.

The Eta Lyrids (ELY) are visible this week from a radiant located at 19:22 (291)
+43. This position lies in extreme eastern Lyra, four degrees southwest of the
third magnitude star Delta Cygni. This shower is active from May 6 through the
14th, peaking on May 11. Rates at maximum activity are near two per hour as seen
from the northern hemisphere. Unfortunately the Eta Lyrid radiant does not rise
very high in the northern sky as seen from the southern hemisphere so
rates seen from below the equator are minimal. Activity from this shower is best
seen during the last hour before dawn when the radiant is situated highest in a
dark sky. With an entry velocity of 43 km/sec., the average Eta Lyrid meteor
would be of medium speed.

The Eta Aquariids (ETA) are particles from Halley’s Comet, produced in
Earth-crossing orbits many centuries ago. We pass closest to these orbits from
May 5 through the 9th. During this period the Eta Aquariids are at their best,
capable of producing ZHR’s of sixty. The actual visible rates are most often
less than half this figure due to the low altitude of the radiant at dawn.
Observed hourly rates at maximum normally vary from zero at 60 degrees north
latitude to 30 near the equator and back down to near zero again in Antarctica,
where the radiant elevation is very low. The radiant is currently located at
22:40 (340) -00. This area of the sky is located in northeastern Aquarius, just
east of the fourth magnitude star Eta Aquarii. 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. No matter your location these meteors will
appear from the eastern sky and shoot in all directions. If the radiant has
sufficient altitude Eta Aquariid meteors can also be seen shooting down toward
the eastern horizon. With an entry velocity of 67 kilometers per second, a
majority of these meteors will appear to move swiftly with a high percentage of
the bright meteors leaving persistent trains. Surprisingly, this shower produces
very few fireballs.

As seen from the mid-northern hemisphere (45N) one would expect to see
approximately ten 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
thirteen 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. Evening rates are slightly 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.