Meteor Activity Outlook for April 9-15, 2011
April 11, 2011
The following is a slightly edited version of Bob Lunsford’s excellent weekly summary of meteor activity. The original version can be found at the American Meteor Society’s site.
Meteor activity picks up a bit during April as two major showers are active during the month. The first of these, the Lyrids, are active from the 16th through the 25th, with a pronounced maximum on the 22nd. The Eta Aquariids start appearing near the 28th and reach maximum activity during the first week in May. 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) rise this month toward a maximum in July.
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.
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 list below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.
Shower Name RA DEC Vel Rates km/s NH SH ANT Antihelions 14h 12m -13 30 2 2 ZCY Zeta Cygnids 20h 08m +41 56 <1 <1 RA - Right Ascension DEC - Declination Vel - Velocity relative to Earth (in km per sec) Rates - Rate of visible meteors per hour from a dark site NH - Northern Hemisphere SH - Southern Hemisphere