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 Wednesday September 1st. At this time the moon will be located ninety degrees west of the sun and will rise near 0100 local daylight time (LDT) for locations in the mid-northern latitudes of the northern hemisphere. This weekend the waning gibbous moon will rise during the late evening hours and remain in the sky the remainder of the night. Meteor observations are difficult under such circumstances unless your sky is transparent. The estimated total hourly rates for evening observers this week is near three from the northern hemisphere and two for observers south of the equator. For morning observers the estimated total hourly rates should be near twelve from the northern hemisphere and eight 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. Morning rates are reduced this week 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 August 28/29. 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 last few remnants from the August Draconids (AUD) may be seen this weeknd. The radiant is currently located at 18:44 (281) +63. This position lies in southern Draco, ten degrees east of the second magnitude star Eltanin (Gamma Draconis). With an entry velocity of 23 km/sec. most of these meteors will appear to move slowly. The radiant is best placed near 2200 Local Daylight Time (10pm LDT) when it lies highest in the sky. Due to its high northern declination this shower is not well seen from the southern hemisphere.
The wide Antihelion (ANT) radiant is now centered at 23:12 (348) -03. This area of the sky lies in western Pisces, three degrees north of the fourth magnitude star Phi Aquarii. 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 eastern Aquarius, southern Pegasus, western Pisces, or western Cetus 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.
The Alpha Aurigids (AUR) is the first radiant of the Perseus-Aurigid complex to become active. Maximum occurs on September 1, so rates this weekend will be very low. Even at maximum with a last quarter moon in the sky, rates will most likely not exceed one shower member per hour. The radiant position at maximum is 06:04 (091) +36. This position lies in eastern Auriga only one degree southeast of the third magnitude star Theta Aurigae. This is different than the old position which was close to Capella (Alpha Aurigae). Video results from the 2007 outburst of this shower showed that a majority of the activity came from the radiant near Theta Aurigae. The radiant is best placed near 0500 LDT, when it lies highest in a dark sky. With an entry velocity of 67 km/sec., most activity from this radiant would be swift. Activity can be seen, if it occurs, from the southern tropic regions during the last few hours before dawn.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately eight 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 five 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. Rates are reduced during the morning hours 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.
|SHOWER||DATE OF MAXIMUM ACTIVITY||CELESTIAL POSITION||ENTRY VELOCITY||CULMINATION||HOURLY RATE||CLASS*|
|RA (RA in Deg.) DEC||Km/Sec||Local Daylight Time||North-South|
|August Draconids (AUD)||Aug 21||18:44 (281) +63||23||22:00||<1 - <1||IV|
|Antihelion (ANT)||-||23:12 (348) -03||30||02:00||2 - 2||II|
|Alpha Aurigids (AUR)||Sep 01||06:04 (091) +36||67||03:00||1 - <1||II|