(meteorobs) Meteor Activity Outlook for April 9-15, 2011

[lunro.imo.usa at cox.net]

During this period the moon reaches its first quarter phase on Monday April 11. At this time the moon will lie ninety degrees west of the sun and will set near 0100 LDT (Local Daylight Time) for those situated in the mid-northern latitudes. This is favorable circumstances for meteor observing as the moon will have set before the active morning hours arrive. The estimated total hourly rates for evening observers this week is near two as seen from the northern hemisphere and three as seen from the southern hemisphere. For morning observers the estimated total hourly rates should be near eleven from the northern hemisphere and sixteen as seen from south of the equator. 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 (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning April 9/10. 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 14:12 (213) -13. This area of the sky lies in eastern Virgo, three degrees south of the fourth magnitude star Kappa Virginis. This radiant is best placed near 0200 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 Libra, eastern Hydra, or eastern Virgo could be a candidate for this shower. Rates at this time should be near two per hour no matter your location. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.

Studies of the IMO video database by Sirko Molau and Juergen Rendtel has revealed a weak radiant active in the constellation of Cygnus this time of year. The Zeta Cygnids (ZCY) are active from March 27 through April 13 with maximum activity occurring on April 6. The current radiant position lies at 20:08 (302) +41. This position lies in central Cygnus, two degrees west of the second magnitude star Sadr (Gamma Cygni). The radiant is best placed during the last dark hour before dawn, when it lies highest above the horizon in a dark sky. Due to the northern declination of the radiant, this activity is not well seen from the southern hemisphere. No matter your location, rates at this time are expected to be less than one per hour. At 44km/sec. the Zeta Cygnids would produce meteors of average velocity.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately nine 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 condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.

Antihelion (ANT) 14:12 (213) -13   Velocity - 30km/sec
Northern Hemisphere - 2 per hour Southern Hemisphere - 2 per hour

Zeta Cygnids (ZCY) 20:08 (302) +41   Velocity - 44km/sec
Northern Hemisphere - <1 per hour Southern Hemisphere - <1 per hour

Clear Skies!

Robert Lunsford
American Meteor Society