(meteorobs) Meteor Activity Outlook for May 2-8, 2008

Robert Lunsford lunro.imo.usa at cox.net
Sat May 3 01:48:44 EDT 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.

Antihelion (ANT) - 15:44 (236) -20   Velocity - 30km/sec.
Northern Hemisphere - 1   Southern Hemisphere - 2

Eta Lyrid (ELY)  18:48 (282) +44   Velocity - 44km/sec.
Northern Hemisphere - 1   Southern Hemisphere - <1

Eta Aquariid (ETA)  22:24 (336) -01   Velocity - 66km/sec.
Northern Hemisphere - 10   Southern Hemisphere - 10

*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




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