(meteorobs) Meteor Activity Outlook for May 2-8, 2009

[Robert Lunsford]

May is a fairly slow month for meteor activity. The Eta Aquariids are very
active the first two weeks 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 waxes from a half illuminated state to nearly
full by the end. This weekend the waxing gibbous moon sets during the early
morning hours allowing a few hours of dark sky observing between moonset and
the start of morning twilight. Later in the period the nearly full moon is
above the horizon nearly the entire night making meteor observations
difficult. The estimated total hourly rates for evening observers this week
is near one as seen from the northern hemisphere and two for those situated
south of the equator. For morning observers the estimated total hourly rates
should be near twelve for those located in the mid-northern hemisphere (45
N) and twenty for those viewing from the mid-southern hemisphere (45 S).
Locations between these two extremes would see activity between the listed
figures. 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 moonlight.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning May 2/3. 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 15:40 (235) -20. This
area of the sky lies in eastern Libra, five degrees northwest of the second
magnitude star Dschubba (Delta Scorpii). This radiant is best placed near
0200 LDT when it is located on the meridian and lies highest in the sky
above the horizon. Due to the large size of this radiant, any meteor
radiating from southeastern Libra, extreme eastern Hydra, southwestern
Ophiuchus, or northwestern Scorpius could be a candidate for this shower.
Rates at this time should be near two per hour as seen from the southern
hemisphere and only one as seen from north of the equator. With an entry
velocity of 30km/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 six years ago this May. Weak activity from
this radiant has been seen in most years from May 6 through May 14, with
maximum activity occurring on May 10. Activity from this source will not be
noticed until late in this period when the radiant position will be located
at 19:12 (288) +45. This area of the sky is located in northeastern Lyra,
five degrees west of the third magnitude star Delta Cygni. 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 43 kilometers
per second, a majority of these meteors will appear to move at moderate
speeds.

The video studies of Sirko Molau have revealed a weak radiant active in
Cygnus this time of year. The Xi Cygnid (XCG) radiant is currently located
at 21:44 (326) +45. This area of the sky is located in eastern Cygnus, very
close to the fourth magnitude star Rho Cygni. Maximum activity occurred on
April 27 so current rates are expected to now be less than one per hour.
These meteors are best seen during the last dark hour before dawn, when the
radiant lies highest above the horizon in a dark sky. This shower is best
seen from the northern hemisphere, where the radiant lies high in the sky at
dawn. At 44 km/sec. the Xi Cygnids will usually produce meteors of medium
velocity.

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 25 near the equator and back down to near zero
again in Antarctica, where the radiant elevation is very low. Hourly rates
this weekend are anywhere from zero to five per hour depending on your
latitude and observing conditions. Rates will increase significantly as the
week progresses as we approach the May 7 maximum. The radiant is currently
located at 22:20 (335) -02. This area of the sky is located in northern
Aquarius, just south of 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 68
kilometers per second, a majority of these meteors will appear to move
swiftly with a high percentage of the bright meteors leaving persistent
trains. More tips on viewing the 2009 Eta Aquariids are available at:
http://www.amsmeteors.org/showers.html#ETA

As seen from the mid-northern hemisphere (45N) one would expect to see
approximately seven Sporadic meteors per hour during the last hour before
dawn as seen from rural observing sites. Evening rates would be near one per
hour. 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. Locations between these two extremes would see
activity between the listed figures. Evening rates are reduced due to
moonlight.

The table below presents a summary of the expected activity this week. Rates
and positions are exact for Saturday night/Sunday morning but may be used
all week.

Antihelion (ANT) - 15:40 (235) -20    Velocity - 30km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - 2

Eta Lyrids (ELY) - 19:12 (288) +45    Velocity - 43km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - <1

Xi Cygnids (XCG) - 21:44 (326) +45    Velocity - 44km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - <1

Eta Aquariids (ETA) - 22:20 (335) -02     Velocity - 68km/sec.
Hourly Rates - Northern Hemisphere 5 - Southern Hemisphere - 5

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#X2009

Clear Skies!
Robert Lunsford
American Meteor Society