(meteorobs) Meteor Activity Outlook for May 24-30, 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 last quarter phase on Wednesday May
28th. At this time the moon will be located ninety degrees west of the the
sun and will rise near 0100 local daylight or summer time (DST). This
weekend will prove difficult to view meteoric activity as the waning gibbous
moon will be in the sky most of the night. With the moon rising later each
evening conditions improve as the week progresses. 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 six. For those located in the mid-southern
hemisphere (45 S) morning rates would be near fourteen and evening rates
near three. 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 lunar interference.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning May 24/25. 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 17:04 (256) -23. This
area of the sky lies in southern Ophiuchus, eight degrees northeast of the
orange first magnitude star Antares (Alpha Scorpii). Actually any meteor
from northern Scorpius, western Sagittarius, as well as southern Serpens
Cauda 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 one for northern observers and two 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 Aquariids (ETA) peaked on May 5 and are near the end of their
activity for 2008. Rates are now less than one per hour no matter your
location. 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 23:32 (353) +07. This area of the sky is located in western
Pisces near the fourth magnitude star Theta 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. 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.

During late May and early June, an occasional long meteor may shoot upwards
from the northeastern horizon just before dawn. Most likely these are
members of the Daytime Arietid (DAR) meteor shower. The radiant lies
approximately thirty degrees west of the sun therefore only a trace of this
shower can ever be seen by the visual observer. Dawn becomes too bright
before the radiant can achieve sufficient altitude to provide a good 
display.

If this shower were visible in a dark sky it would be among the strongest
displays of the year. This shower is the strongest daylight/radio shower of
the year. The current position of the radiant is 02:20 (035) +16. This
position lies in western Aries, seven degrees southeast of the second
magnitude star Hamal (Alpha Arietis). Seeing any activity from this display
would be extremely lucky this week. Prospects improve as we approach the
June 7 maximum.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are low,
but fairly steady. One would expect to see approximately five 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 twelve per hour as seen from rural
observing sites and three per hour during the evening hours. Moonlight
interferes during the morning 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) - 17:04 (256) -23 Velocity - 30km/sec.
Northern Hemisphere - 1   Southern Hemisphere - 2

Eta Aquariid (ETA)  23:32 (353) +07 Velocity - 66km/sec.
Northern Hemisphere - <1   Southern Hemisphere - <1

Daytime Arietid (DAR)  02:20 (035) +16 Velocity - 37km/sec.
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#X2008

Clear Skies!
Robert Lunsford
American Meteor Society