(meteorobs) Meteor Activity Outlook for August 25-31, 2012

[Robert Lunsford]

During this period the moon reaches its full phase on Friday August 31st. At this time the moon will be located opposite the sun and will be above the horizon all night long. This weekend the waxing gibbous moon will set during the early morning hours, allowing a few hours of dark skies between moon set and the start of morning twilight in which good activity can be observed. The estimated total hourly meteor rates for evening observers this week is near four for observers located at mid-northern latitudes and three for observers in mid-southern latitudes. For morning observers the estimated total hourly rates should be near twenty from the mid-northern hemisphere and eight from the mid-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. Evening rates are reduced during this period 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 25/26. 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 radiants are expected to be active this week:

The Kappa Cygnids (KCG) are winding down but still active from a wide radiant located at 18:28 (268) +63. This position lies in a remote area of southern Draco. The nearest bright star is third magnitude Aldib (Delta Draconis), which lies seven degrees to the northeast. Some readers will notice that this position is west of that given last week. The reason for this seemingly retrograde motion is the different sub-centers of activity that appear within the large radiant area during this month. Observers need not be strict with shower association for this shower due to the wide radiant and these sub-centers of activity. Maximum activity occurred on August 18th so current rates would be less than one per hour no matter your location. With an entry velocity of 23 km/sec. most of these meteors will appear to travel slower than average. The radiant is best placed near 2300 Local Daylight Time (LDT) 11pm Local Daylight Time (LDT) when it lies nearly overhead for much of the Northern Hemisphere. Due to its high northern declination this activity is not well seen from the southern hemisphere.

The large Antihelion (ANT) radiant is currently located at 23:00 (345) -05. This position lies in northeastern Aquarius, four degrees northwest of the fourth magnitude star Phi Aquarii. Due to the large size of this radiant, Antihelion activity may also appear from eastern Capricornus, southern Pisces, southern Pegasus, and western Cetus as well as Aquarius. 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 are expected to be near one per hour no matter your location. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

There is an active yet unnamed radiant located just east of the "circlet" of Pisces this week. The exact location for Sunday morning is 23:48 (357) +06. This lies in western Pisces between the fourth magnitude stars Omega and Iota Piscium. Radiant drift per day averages 0.8 degree in right ascension and +0.4 in declination. This radiant is stronger than all but the Perseids so naked eye verification should be fairly easy. This activity is present from August 6th through September 6th with a maximum occurring on August 17th. With an entry velocity of 41 km/sec., most activity from this radiant would be of average velocities.

There is another active yet unnamed radiant located in southern Perseus active only this weekend The exact location for Sunday morning is 03:52 (058) +36. This position lies two degrees west of the fourth magnitude star Xi Persei. This is the fourth most active radiant in the sky so rates would be near one per hour as seen during the morning hours from the mid-northern hemisphere. This radiant is not well placed for viewing south of the equator. With an entry velocity of 69 km/sec., most activity from this radiant would appear as swift meteors.

The Perseids (PER) peaked on Sunday August 12th, producing visible hourly rates near 50 as seen from dark skies. They are still the most active radiant in the sky but rates are now down to only 2-3 shower members per hour as seen from the mid-northern hemisphere during the early morning hours. The current radiant is located at 04:28 (067) +59. This position lies in a blank portion of southern Camelopardlis, five degrees southeast of fourth magnitude star Beta Camelopardalis. With an entry velocity of 61 km/sec., most activity from this radiant would be swift.

The Aurigids (AUR) become active on August 25th but are very weak until the morning of August 30th. Maximum occurs on August 31st when it becomes the most active radiant in the sky. Unfortunately the full moon will spoil the display at this time so only 1-2 shower members will be visible per hour as seen during the morning hours from mid-northern latitudes. Very little activity would be visible from the southern hemisphere. At maximum the radiant is located at 06:02 (091) +39, which places it in eastern Auriga just two degrees north of third magnitude Theta Aurigae. With an entry velocity of 67 km/sec., most activity from this radiant would be swift.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately fourteen 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. Evening rates are reduced due to to moonlight during this period.

The list below presents a summary of the expected activity this week. Rates and
positions are exact for Saturday night/Sunday morning August 25/26, but may be
used all week.

Kappa Cygnids (KCG) - 18:28 (268) +63   Velocity 23km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Antihelions (ANT) - 23:00 (345) -05   Velocity 30km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 1 per hour

23:48 (357) +06   Velocity 41km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 1 per hour

03:52 (058) +36   Velocity 69km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - <1 per hour

Perseids (PER) - 04:28 (067) +59   Velocity 61km/sec
Northern Hemisphere - 3 per hr    Southern Hemisphere - 1 per hour

Aurigids (AUR) - 06:02 (091) +39   Velocity 67km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society