(meteorobs) Meteor Activity Outlook for May 15-21, 2010

[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 weak Nu Cygnids, 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 first quarter phase on Thursday May 20th. At this time the moon lies ninety degrees east of 
the the sun and sets near 0100 local daylight time. This weekend the waxing crescent moon will set during the early evening hours 
but will not interfere with meteor observing during the more active morning hours. The estimated total hourly rates for evening 
observers this week is near two for northern observers and four for those viewing from south of the equator. For morning observers 
the estimated total hourly rates should be near ten from the northern hemisphere and nineteen as seen from the southern hemisphere. 
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 slightly reduced due to moonlight.

The radiant (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday 
night/Sunday morning May 15/16. 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 16:32 (248) -22. This area of the sky lies in southern Ophiuchus some five 
degrees north of the first magnitude orange star Antares (Alpha Scorpii). This radiant is best placed near 0200 local daylight time 
(LDT) when it lies on the meridian and is located highest in the sky. Due to the large size of this radiant, any meteor radiating 
from eastern Libra, northern Lupus, southern Ophiuchus, or Scorpius could be a candidate for this shower. Rates at this time should 
be near one per hour as seen from the northern hemisphere and two per hour as seen from 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) are particles from Halley's Comet, produced in Earth-crossing orbits many centuries ago. We passed closest 
to these orbits from May 5 through the 9th. Hourly rates this weekend are anywhere from zero to five per hour depending on your 
latitude and observing conditions. Rates will slowly decrease as we move further away from the May 7 maximum. The radiant is 
currently located at 23:00 (345) +02. This area of the sky is located in northeastern Aquarius, just one degree east of the fourth 
magnitude 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 down toward the eastern horizon. With an entry 
velocity of 67 kilometers per second, a majority of these meteors will appear to move swiftly with a high percentage of the bright 
meteors leaving persistent trains. Surprisingly, this shower produces very few fireballs.

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 slightly 
reduced due to moonlight.

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

Antihelion (ANT) - 16:32 (248) -22     Velocity - 30km/sec.
Northern Hemisphere - 1 per hr.   Southern Hemisphere - 2 per hr.

Eta Aquariids (ETA) - 23:00 (345) +02    Velocity - 67km/sec.
Northern Hemisphere - 2 per hr.   Southern Hemisphere - 3 per hr.

*For a detailed explanation on the different classes of meteor showers and other astronomical terms, please visit: 
http://www.amsmeteors.org/showers.html#X2010

Clear Skies!
Robert Lunsford
American Meteor Society