During this period the moon reaches its last quarter phase on Sunday August 17th. At this time the moon is located 90 degrees west of the sun and will rise between midnight and 0100 local daylight time as seen from mid-northern locations. Later this week the waning crescent moon will rise later in the morning increasing the window of opportunity to view under totally dark skies. The estimated total hourly meteor rates for evening observers this week is near 5 as seen from the northern hemisphere and 3 as seen from southern tropical latitudes. For morning observers the estimated total hourly rates should be near 25 for observers located in mid-northern latitudes and 15 for south tropical observers. 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 during this period will are lower than normal due to moonlight. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.
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 16/17. 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.
These sources of meteoric activity are expected to be active this week:
The Kappa Cygnids (KCG) are active during this period from a wide radiant located near 19:04 (286) +59. This location lies actually lies in southern Draco, 6 degrees northwest of the 4th magnitude star known as Kappa Cygni. Consider this position the center of a large radiant rather than a sharp point. Even though maximum activity is predicted to occur on August 18th, current rates would still 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. Despite the low rates seen from this source, this shower is known to be a producer of fireball class meteors.
The center of the large Anthelion (ANT) radiant is currently located at 22:28 (337) -08. This position lies in central Aquarius, just east of the faint star known as Theta Aquarii. These meteors may be seen all night long but the radiant is best placed near 0100 LDT when it lies on the meridian and is positioned highest in the sky. Due to the large radiant area, meteors from this source may also appear to radiant from southwestern Pegasus, eastern Capricornus, and western Pisces as well as Aquarius. Rates at this time should be near 2 per hour no matter you location. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.
The Theta Piscids (TPI) are a newly discovered radiant originally reported by SonotaCo in 2009 as the August Beta Piscids (BPI). The BPI’s have since been removed from the IAU list as researchers there feel it was a synonymous with the North Delta Aquariids, a shower no longer recognized by the IMO. Studies of the IMO video database has shown that this radiant is active between August 8 and September 1. Researchers have not been able to determine a date of maximum activity as the activity profile remains flat throughout the entire activity period. The midpoint of this source occurs on August 20 when the radiant lies at 23:28 (352) +04. This position is located directly in the “Circlet” of Pisces in the western end of the constellation. This position lies close to both the Anthelion and the Delta Aquariid radiants so care must be taken to distinguish between these radiants. The IMO database contains a hefty 4500 members of this shower so expected rates should be 1-2 shower members per hour when the radiant lies highest in the sky, which occurs near 0300 LDT. This source is seen equally well from both hemispheres. With an entry velocity of 39 km/sec., most activity from this radiant would be of average velocities. Visual observations of this source should be undertaken to see if it stands out from the Anthelion source or should be included as part of the Anthelions. Curiously, if one extends the radiant drift of the Southern Taurids back into August, the position of right ascension (celestial longitude) is a close match. The declination (celestial latitude) though lies too far south to be a good match.
The Delta Aquariids (SDA) are still active from a radiant located at 23:49 (357) -11. This position is located in eastern Aquarius 3 degrees north of the faint star known as Omega 2 Aquarii. Hourly rates have fallen to only 1 per hour as seen from the northern hemisphere and 2 per hour as seen from south of the equator. 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.
IMO Shower #136 is part of the Perseus-Auriga complex of radiants that are active from late August through early October. This is much like the Centaurus complex of late January through early March in that it involves several weak, diffuse radiants that don’t amount to much by themselves, but added together can add 5-10 meteors per hour to the overall activity during the morning hours when they lie high in the sky. This particular radiant was discovered among the data of the IMO network and is best seen from August 18-25. The mean position of this radiant lies near 02:08 (032) +41. This position is located in eastern Andromeda just southeast of the famous double star known as Almach (Gamma Andromedae). Activity is weak even at maximum (August 25), but keen observers may be able to spot 1 shower member per hour between midnight and dawn as seen from the northern hemisphere. This source is not well seen from the southern hemisphere as it does not rise very high in the sky. With an entry velocity of 46 km/sec., most activity from this radiant would be of average velocities.
The last of the Eta Eridanids (ERI) are expected to be seen this weekend from a radiant located at 03:20 (050) -08 . This location lies in western Eridanus, 3 degrees northwest of the faint star known as Epsilon Eridani. Hourly rates have now fallen to less than 1 no matter your location. The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. With an entry velocity of 66 km/sec., most activity from this radiant would be swift with persistent trains on the brighter meteors. These meteors have been a highlight of my recent observing sessions and I hope to see a couple more before they are finished for the year.
The Perseids (PER) are still active from a radiant located at 03:36 (054) +59. This position actually lies in eastern Camelopardalis, 9 degrees north of the 2nd magnitude star known as Mirfak (Alpha Persei). The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. Current rates would be near 10 per hour as seen from the northern hemisphere and perhaps half this many as seen from south of the equator. Activity from this source is not visible south of 40 degrees south latitude. With an entry velocity of 61 km/sec., most activity from this radiant would be swift with a large percentage of persistent trains produced by the brightest meteors.
The last of the Alpha Triangulids (ATR) are expected this week from a radiant located at 03:36 (054) +36. This position lies in the southern Perseus, 6 degrees southeast of the famous eclipsing variable star known as Algol (Beta Persei). This source of meteors is best seen from July 25 through August 20 with maximum activity occurring on July 27. Hourly rates should be less than 1 no matter your location. The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. With an entry velocity of 68 km/sec., most activity from this radiant would be swift.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately 10 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 4 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 5 per hour as seen from rural observing sites and 2 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning rates are reduced due to interfering moonlight.
The table below presents a list of radiants that are expected to be active this week. Rates and positions are exact for Saturday night/Sunday morning except where noted in the shower descriptions.
|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 18||19:04 (286) +59||23||23:00||<1 – <1||II|
|Anthelions (ANT)||–||22:28 (337) -08||29||02:00||2 – 2||II|
|Theta Piscids (TPI)||Aug 20||23:28 (352) +04||39||03:00||1 – 1||IV|
|Delta Aquariids (SDA)||Jul 30||23:49 (357) -11||42||03:00||1 – 2||I|
|IMO #136||Aug 25||02:08 (032) +41||46||05:00||1 – <1||IV|
|Eta Eridanids (ERI)||Aug 04||03:20 (050) -08||66||06:00||<1 – <1||IV|
|Perseids (PER)||Aug 13||03:36 (054) +59||61||06:00||10 – 5||I|
|Alpha Triangulids (ATR)||Aug 08||03:36 (054) +36||67||06:00||<1 – <1||IV|