Meteor Activity Outlook for September 17-23, 2011
September 17, 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.
September offers longer nights in the northern hemisphere that tend to be less hazy than those experienced in mid-summer. In the sky, no major showers are visible from either hemisphere but the northern hemisphere enjoys the advantage of higher sporadic rates. Most of the shower activity this month is produced from the Perseus-Aurigid complex active this time of year. These showers rarely produce more than five meteors per hour but still manage to produce most of the shower activity seen this month. Unfortunately the Perseus-Aurigid complex lies too low in the northern sky for southern hemisphere observers to view very well. Video studies have shown that the Southern Taurids are visible as early as September 7th therefore after this date the Antihelion radiant will no longer be listed until the Taurid showers end in December. The Antihelion meteors are still active but their radiant is superimposed upon that of the more numerous Taurids, therefore it is impossible to properly separate these meteors. Observers in the southern hemisphere suffer from some of their lowest rates of the year this month. The Southern Taurid radiant is not too badly placed so observers south can expect to see a little of this activity this month.
During this period the moon reaches its last quarter phase on Tuesday September 20th. At this time the moon will lie ninety degrees west of the sun and will rise near 0100 local daylight time (LDT) as seen from mid-northern latitudes. This weekend the waning gibbous moon will interfere with meteor observing during the morning hours. Skies will be dark during the early evening hours until moon rise, which will occur during the late evening hours. It would be better to wait until later this week to view meteor activity, when the moon becomes less bothersome. The estimated total hourly rates for evening observers this week is near four as seen from the northern hemisphere and two as seen from the southern hemisphere. For morning observers the estimated total hourly rates should be near nine as seen from mid-northern latitudes and six from mid-southern latitudes. 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. Morning 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 September 17/18. 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 Southern Taurid (STA) radiant is now centered at 01:08 (017) +05. This area of the sky lies in southern Pisces, three degrees north of the fourth magnitude star Epsilon Piscium. This radiant is best placed near 0200 LDT, when it lies on the meridian and is located highest in the sky. Rates at this time should be near two per hour no matter your location. With an entry velocity of 27 km/sec., the average Southern Taurid meteor would be of medium-slow speed.
Many radiants in the region of Eridanus have been suspected this time of year. Recent studies of the IMO’s video database by Sirko Molau and Juergen Rendtel has verified a radiant active in Eridanus from September 3rd through the 24th with maximum activity occurring on the 7th. The Nu Eridanid (NUE) radiant is currently located at 04:53 (073) +06. This position lies in western Orion near the third magnitude star Pi 3 Orionis. The radiant is best placed during the last hour before the start of morning twilight. Rates may be close to one per hour this week. With an entry velocity of 68 km/sec., most activity from this radiant would be swift. With the radiant lying close to the celestial equator, these meteors are seen equally well from both hemispheres.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately six sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near three per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near three per hour as seen from rural observing sites and one per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning rates are reduced by 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 STA Southern Taurids 01h 08m +05 27 2 2 NUE nu Eridanids 04h 53m +06 68 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