During this period the moon reaches its first quarter phase on Saturday August 6th. At this time the moon will lie ninety degrees east of the sun and will set near 0100 local daylight time (LDT) for observers located in the mid-northern latitudes. Next week the waxing gibbous moon will enter the morning sky and will reduce the observing window for dark sky viewing with each passing night. The estimated total hourly rates for evening observers this week is near five 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 twenty eight from mid-northern latitudes and seventeen from mid-southern latitudes.Â 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 6/7. 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:
Activity from the August Draconids (AUD) can be first detected near August 11th from a radiant located at 18:00 (270) +61. This position lies in southern Draco, close to the second magnitude star Eltanin (Gamma Draconis). Maximum activity is not predicted until August 21st so current rates would be low, less than one per hour. 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 Kappa Cygnids (KCG) are active from a wide radiant located in northern Lyra, southern Draco, and northwestern Cygnus. The strongest areas seem to vary year to year but the current mean value lies near 18:47 (282) +46. This location lies in northern Lyra, seven degrees northeast of the brilliant star Vega (Alpha Lyrae). Maximum activity is now predicted to occur on August 14th. 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 LDT (11pm 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. Of the few meteors seen from this source, several of them have been of fireball class brightness.
The Alpha Capricornids (CAP) are active from a wide radiant located at 20:40 (310) -08. This position lies near the area where Capricornus, Aquarius, and Aquila meet. This position lies eight degrees northeast of the third magnitude double star Alpha Capricornii. The radiant is best placed near 0100 local daylight time (LDT), when it lies on the meridian and is highest in the sky.Â Maximum activity occurred on July 30th so current rates should be less than one as seen from the northern hemisphere and one per hour from the southern. Don’t confuse these meteors with the antihelion meteors, which have a radiant just to the east. Both radiants need to be in your field of view to properly sort these meteors. With an entry velocity of 25 km/sec., most activity from this radiant would be slow, a bit slower than the antihelions. This radiant is well seen except for far northern latitudes where it remains twilight all night long and the radiant does not rise as high into their sky.
The wide Antihelion (ANT) radiant is now centered at 21:48 (327) -12. This area of the sky lies in eastern Capricornus, three degrees north of the third magnitude star Deneb Algedi (Delta Capricorni). 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 Capricornus, Aquarius, or southwestern Pegasus could be a candidate for this shower. Rates at this time should be near one per hour as seen from the northern hemisphere and two per hour as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.
The Delta Aquariids (SDA) reached maximum activity on July 30th. Current hourly rates are near two per hour as seen from the northern hemisphere and three per hour as seen from south of the equator. The radiant is currently located at 23:09 (347) -14. This position lies in central Aquarius, three degrees northeast of the third magnitude star Delta Aquarii. The radiantÂ 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..
The Piscids Austrinids (PAU) are a minor shower not well seen from the northern hemisphere. This radiant is active from July 15 through August 10. Maximum activity occurred on July 28 when the zenith hourly rate (ZHR) may reach five. These rates are only seen from the southern hemisphere where the radiant passes overhead. From mid-northern latitudes, rates of one per hour at maximum are usually seen. The radiant is currently located at 23:18 (350) -27. This position lies in extreme northwestern Sculptor, four degrees northeast of the first magnitude star Fomalhaut (Alpha Piscis Austrinus). The radiant is best placed near 0300 LDT, when it lies highest in the sky. With an entry velocity of 35km/sec., most activity from this radiant would be of average velocities.
Studies by Sirko Molau and Juergen Rendtel of the IMO’s video data have revealed an active radiant in the constellation of Pisces this time of year. The August Piscids (AUP) are active from August 2nd through the 9th with maximum activity occurring on the 4th. On the 4th, the radiant is located at 00:40 (010) +19. This area of the sky lies in a remote area of central Pisces, five degrees northeast of the second magnitude star Algenib (Gamma Pegasi). Interestingly, if one were to continue the radiant drift for the July Pegasids into August, it would closely match that of the August Piscids. This radiant is best placed during the last dark hour before dawn, when it lies highest above the horizon in a dark sky. Rates at this time should be less than one no matter your location. With an entry velocity of 66 km/sec., the average August Piscid meteor would be of swift speed.
The Perseids (PER) are active from a radiant located at 02:38 (040) +56. This position lies in northern Perseus, just west of the fourth magnitude star Eta Persei.Â The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. Hourly rates this weekend during the late morning hours would be near ten as seen from the northern hemisphere . As the week progresses the rates will increase as we approach the August 13 maximum. Unfortunately the dark viewing window of opportunity decreases as the moon waxes and the moon sets later with each passing night. Activity from this source is poorly seen from the southern hemisphere and not visible at all south of 40 degrees south latitude.Â With an entry velocity of 61 km/sec., most activity from this radiant would be swift.
While viewing the Perseids through the years, many observers have reported noticing weak activity from the area of Cetus and Eridanus. During their studies of the IMO’s video database,Â Sirko Molau and Juergen Rendtel discovered an active radiant in this area. The Eridanids (ERI) are active from August 4th through the 18th with maximum activity occurring on the 9th. Hourly rates could reach 2-3 per hour at maximum. The radiant is currently located at 02:53 (043) -12. This area of the sky is located in extreme western Eridanus, between the faint stars Pi and Eta Eridani. This radiant is best placed during the last hour before dawn when it lies highest in a dark sky. With an entry velocity of 64 km/sec., the average Eridanid meteor 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 two per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near seven 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. Evening rates are reduced this week 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||18:00 (270) +61||23||22:00||<1 – <1||IV|
|Kappa Cygnids (KCG)||Aug 14||18:47 (282) +46||23||23:00||<1 – <1||IV|
|Alpha Capricornids (CAP)||Jul 30||20:40 (310) -08||25||01:00||<1 – 1||II|
|Antihelions (ANT)||–||21:48 (327) -12||30||02:00||1 – 2||II|
|Delta Aquariids (SDA)||Jul 30||23:09 (347) -14||42||03:00||2 – 3||I|
|Piscis Austrinids (PAU)||Jul 28||23:18 (350) -27||35||03:00||<1 – 1||II|
|August Piscids (AUP)||Aug 04||00:40 (010) +19||66||04:00||<1 – <1||IV|
|Perseids (PER)||Aug 13||02:38 (040) +56||61||06:00||10 – 2||I|
|Eridanids (ERI)||Aug 09||02:53 (043) -12||64||06:00||1 – 1||IV|