Meteor Activity Outlook for May 2-8, 2008

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 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 its new phase
on Monday May 5th. At this time the moon will be located near the sun and will not
be visible at night. 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 twenty. For those located in the
mid-southern hemisphere (45 S) morning rates would be near twenty six 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.

The radiant positions and rates listed below are exact
for Saturday night/Sunday morning May 3/4. 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 15:44 (236) -20. This
area of the sky lies in eastern Libra, five degrees west of the 3rd magnitude star
Acrab (Beta Scorpii). Actually any meteor from northwestern Scorpius, southern
Ophiuchus, as well as Libra could be a candidate for this shower. This radiant is
best placed near 0200 LDT time 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 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 18:48 (282) +44. This area of the sky is located in northern Lyra, five
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) are particles from Halley’s Comet, produced in
Earth-crossing orbits many centuries ago. We pass closest to these orbits from
May 3 through the 7th. 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
25 near the equator and back down to near zero again in Antarctica, where the
radiant elevation is very low. Hourly rates are now anywhere from zero to twenty
per hour depending on your latitude and observing
conditions. The radiant is currently located at 22:24 (336) -01. This area of the
sky is located in northern Aquarius, close to the fourth magnitude star Gamma
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 down 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.

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