During this period the moon reaches its first quarter phase on Friday August 24th. At this time the moon will be located ninety degrees east of the sun and will set near midnight local daylight time (LDT). This weekend the waxing crescent moon will set during the early evening hours and will not interfere with meteor observing during the more productive morning hours. 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 two from the mid-northern hemisphere and twelve 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.
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 18/19. 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 active from a wide radiant located at 18:28 (277) +59. This position lies in Draco, ten degrees northeast of the second magnitude star Eltanin (Gamma Draconis). 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 occurs on August 18th so current rates would be near two per hour from the northern hemisphere and less than one shower member per hour from south of the equator. 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 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 22:36 (339) -07. This position lies in central Aquarius, four degrees northeast of the fourth magnitude star Sadalsuud Sadalsuud (Beta Aquarii). Due to the large size of this radiant, Antihelion activity may also appear from eastern Capricornus, western Pisces, and southern Pegasus, 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 two 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 within the “circlet” of Pisces this week. The exact location for Sunday morning is 23:27 (352) +04. 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 and the Antihelons 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.
The Delta Aquariids (SDA) are near the end of their activity for 2012. They are still weakly active from a radiant located at 23:54 (359) -11. This position is located on the Aquarius/Cetus border, four degrees northeast of the Omega 2 Aquarii. Current hourly rates would be less than one no matter your location. The radiant is best placed near 0300 LDT, when it lies highest in the sky. With an entry velocity of 42 km/sec., most activity from this radiant would be of average velocities.
There is another active yet unnamed radiant located close to Almach (Gamma Andromedae) this week. The exact location for Sunday morning is 02:04 (031) +41. Radiant drift averages 0.7 degree in right ascension and -0.3 in declination per day. This radiant is probably the weakest of all listed this week, yet with careful monitoring, several of these meteors should be visible each night . This activity is present from August 18th through the 25th with the maximum occurring on the 25th. 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 weakly active from a radiant located at 03:47 (057) +59. This position lies in southwestern Camelopardlis, ten degrees northeast of the second magnitude star Mirfak (Alpha Persei). Current rates would be near five per hour from theÂ northern hemisphere and two per hour as seen from south of the equator. With an entry velocity of 61 km/sec., most activity from this radiant would be swift.
A new source found by the IMO video cameras to be active this time of year are the Alpha Triangulids (ATR). This radiant has recently been found to be active later than previously published, with the activity period ranging from July 25 through August 21 with maximum activity occurring on July 27. Current rates would be less than one per hour, no matter your location. The radiant is currently located at 03:44 (056) +38, which is actually situated in southern Perseus, four degrees southwest of Epsilon Persei. The radiant is best placed during the last hour before dawn, when it lies highest in a dark sky. With an entry velocity of 67 km/sec., the average Alpha Triangulid meteor would be swift.
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 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.
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|
|Kappa Cygnids (KCG)||Aug 17||18:28 (277) +59||23||23:00||2 – <1||II|
|Antihelions (ANT)||-||22:36 (339) -07||30||02:00||2 -2||II|
|Aug 17||23:27 (352) +04||41||03:00||2 – 2||IV|
|Delta Aquariids (SDA)||July 29||23:54 (359) -11||42||03:00||<1 – <1||I|
|Aug 25||02:04 (031) +41||69||05:00||<1 – <1||IV|
|Perseids (PER)||Aug 12||03:47 (057) +59||61||06:00||5 – 2||I|
|Alpha Triangulids (ATR)||July 27||03:44 (056) +38||67||06:00||<1 – <1||IV|