Meteor Activity Outlook for September 20-26, 2008

September offers longer nights and cooler temperatures in the northern hemisphere. In the sky, no major showers are visible from either hemisphere but the northern hemisphere enjoys the advantage of higher sporadic rates. The two recognized minor showers active in early September have high northern declinations (celestial latitude) therefore are much better suited to be viewed from locations north of the equator. Toward the end of the month the antihelion radiant becomes entangled with the two Taurid radiants and it is impossible to separate them. Therefore the antihelion radiant will be excluded from the list from the last week of September until the end of the Taurid activity period late in November. Observers in the southern hemisphere suffer from some of their lowest rates of the year this month. The Taurid radiants are not too badly placed so observers south of the equator can expect to see a little of this activity toward the end of the month.

During this period the moon reaches its last quarter phase on Monday September 22nd. At this time the moon will rise near 0100 local daylight time (LDT) and will remain in the sky the remainder of the morning. As the week progresses the waning crescent moon will rise later in the morning and will become less of a nuisance. The estimated total hourly rates for evening observers this week is near three for those located in the mid-northern hemisphere (45 N) and one for those viewing from the mid-southern hemisphere (45 S). For morning observers the estimated total hourly rates should be near twelve for those located in the mid-northern hemisphere (45 N) and six for those viewing from the mid-southern hemisphere (45 S). Locations between these two extremes would see activity between the listed figures. These rates assume that you are watching from rural areas away from all sources of light pollution. 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. Rates are reduced during the morning hours due to moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning September 20/21. 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 large Antihelion (ANT) radiant is now centered at 00:44 (011) +05. This area of the sky lies in southern Pisces, two degrees south of the fourth magnitude Delta Piscium. Actually, the radiant is so large that any meteor from northeastern Aquarius, Pisces, southeastern Pegasus, or northern Cetus could be a candidate for this shower. This radiant is best placed near 0200 LDT when it lies on the meridian and is highest in the sky. Hourly rates at this time should be near two no matter your location. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.

The Delta Aurigids (DAU) are present in the morning skies in the second half of September and early October. Maximum activity occurs on October 3rd with an average ZHR of two. Current rates will be most likely less than one per hour. The radiant is currently located 04:48 (072) +48. This position lies in northeastern Perseus, five degrees northwest of the zero magnitude star Capella (Alpha Aurigae). At 64km/sec., the average Delta Aurigid is swift.

Sirko Molau's study of video radiants has shown an active radiant located in Orion during this period. The September Alpha Orionids (AOR) peak on September 27th with a radiant located near 05:24 (081) +07. The area of the sky is located in northwestern Orion near the bright star Bellatrix (Gamma Orionis). Activity is more than a ZHR of one between September 24th and the 30th. This radiant was one of the strongest new showers detected in the video survey so visual detection should be easy later in this period. Meteors from this radiant are not visible during the evening hours as Orion lies beneath the horizon during this time. The radiant gains altitude during the morning hours and is most favorably located near 0600 LDT when it lies highest above the horizon. Due to its location near the celestial equator, activity is visible nearly everywhere. Tropical locations are favored as the radiant passes overhead. Hourly rates this week would be less than one, increasing next weekend. With an entry velocity of 59 km/sec., most members of the September Alpha Orionids would possess a swift velocity.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately ten 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. Moonlight reduces rates during the morning hours this week from all locations.

The table below presents a summary of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning but may be used all week.