(meteorobs) Meteor Activity Outlook for May 10-16, 2008

[Robert Lunsford]

May is a fairly slow month for meteor activity. The Eta Aquariids are very
active the first week 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 2-3 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 its first quarter phase on Monday May
12th. At this time the moon will be located ninety degrees east of the the
sun and will set near 0100 local daylight or summer time (DST). As seen from
the mid-northern hemisphere (45 N) the estimated total hourly rates during
the evening observers would be only one. For morning observers the estimated
total hourly rates should be near twelve. For those located in the
mid-southern hemisphere (45 S) morning rates would be near twenty and
evening rates near two. 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.
Evening rates are reduced due to lunar interference.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning May 10/11. 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 large Antihelion (ANT) radiant is now centered at 16:12 (243) -21. This
area of the sky lies in northwestern Scorpius, seven degrees northwest of
the orange first magnitude star Antares (Alpha Scorpii). Actually any meteor
from northwestern Scorpius, southern Ophiuchus, northern Lupus as well as
eastern Libra 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.
Rates at this time should be near two for northern observers and three for
observers 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 produced by comet IRAS-Araki-Alcock, which passed
very close to the Earth twenty five years ago this May. Weak activity from
this radiant has been seen in most years from May 3 through May 12, with
maximum activity occurring on May 8. The current radiant position is located
at 19:16 (289) +44. This area of the sky is located in on the Lyra/Cygnus
border, eight degrees northeast of the zero magnitude star Vega (Alpha
Lyrae). 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 44 kilometers per second, a majority of these meteors will
appear to move at moderate speeds.

The Eta Aquariids (ETA) peaked last week and are now on the declining side
of their activity profile. Rates as high as five per hour could still be
seen in tropical areas during the last dark hour of the night. In other
locations hourly rates of 1-3 can be expected during that same period. Since
the radiant lies only sixty degrees west of the sun, meteors from this
shower are not visible prior to 0200 LDT. The radiant is currently located
at 22:44 (341) +01. This area of the sky is located in extreme northern
Aquarius, two degrees northeast of the faint star Eta Aquarii. The best time
to view this activity is just 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
downward toward the eastern horizon. With an entry velocity of 66 kilometers
per second, a majority of these meteors will appear to move swiftly with a
high percentage of the bright meteors leaving persistent trains.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are low,
but fairly steady. One would expect to see approximately seven random
meteors during the last hour before dawn from rural observing sites and only
one per hour during the evening hours. As seen from the mid-southern
hemisphere (45S) morning rates would be near fourteen per hour as seen from
rural observing sites and two per hour during the evening hours. Moonlight
interferes slightly during the evening hours.

The table below presents a condensed version of the expected activity this
week. Rates and positions are exact for Saturday night/Sunday morning.

Antihelion (ANT) - 16:12 (243) -21   Velocity - 30 km/sec.
Northern Hemisphere - 2   Southern Hemisphere - 3

Eta Lyrid (ELY)  19:16 (289) +44   Velocity - 44 km/sec.
Northern Hemisphere - 1   Southern Hemisphere - <1

Eta Aquariid (ETA)  22:44 (341) +01   Velocity - 66 km/sec.
Northern Hemisphere - 2   Southern Hemisphere - 2

*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