(meteorobs) Meteor Activity Outlook for August 17-23, 2013

[Robert Lunsford]

During this period the moon reaches its full phase on Wednesday August 21st. At this time the moon is located opposite the sun and interferes with meteor observing all night long. This weekend the waxing gibbous moon will be in the sky until the late morning hours, allowing a small window of opportunity to view under dark skies before dawn interferes. The estimated total hourly meteor rates for evening observers this week is near four for observers located in the northern hemisphere and three for those viewing south of the equator. For morning observers the estimated total hourly rates should be near twenty as seen from mid-northern latitudes and near twelve for observers viewing from tropical southern latitudes. 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 during the evening hours will be reduced 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 17/18. 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 sources of meteoric activity are expected to be active this week:

The Kappa Cygnids (KCG) reach maximum activity this weekend from a wide radiant located at 18:28 (277) +58. This location actually lies in extreme southeastern Draco, eight degrees northeast of the second magnitude star Eltanin (Gamma Draconis) . Despite being at maximum activity, current rates are expected to 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 22:32 (338) -07. This position lies in north-central Aquarius, eight degrees southeast of the star known as Sadalmelik (Alpha Aquarii). Due to the large, oval-shaped radiant, activity from this source may also be seen coming from eastern Capricornus, southwestern Pegasus, and western Pisces as well as Aquarius. These meteors may be seen all night long but the radiant is best placed near 0200 LDT when it lies on the meridian and is located highest in the sky. Rates at this time should be near two per hour regardless of your location. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.

A new source found by IMO video cameras to be active this time of year are the Theta Piscids (TPI). These meteors are active from August 8 through September 1, with maximum activity occurring on August 20. The radiant is currently located at 23:20 (350) +03. This position lies in extreme western Pisces, just inside of the faint circle of stars known as the "Circlet" and just east of the fourth magnitude star known as Gamma Piscium. Hourly rates will be low, most likely less than one per hour no matter your location. These meteors are best seen near 0200 when the radiant lies highest above the horizon. With an entry velocity of 41 km/sec., most activity from this radiant would be of average velocities.

The last of the Delta Aquariids (SDA) for 2013 will be seen this week. This shower reached maximum activity on July 30th and the radiant is currently located at 23:52 (358) -11. This position is located in a blank region of eastern Aquarius, five degrees southwest of the fourth magnitude star known as Iota Ceti. Hourly rates will most likely be less than one per hour, no matter your location. The radiant culminates near 0300 LDT. With an entry velocity of 42 km/sec., most activity from this radiant would be of average velocities.

There is an new unnamed source of meteors active this week from a radiant located at 02:04  (031) +42. IMO shower #136 is active from August 18-25, with maximum activity occurring on August 25. The radiant is located in eastern Andromeda, very close to the spot occupied by the famous second magnitude double star known as Almach (Gamma Andromedae).  This area of the sky is best placed in the sky during the last hour before dawn, when it lies highest above the horizon in a dark sky. With an entry velocity of 46 km/sec., most activity from this radiant would be of average velocities.

The Perseids (PER) reached maximum activity on August 12 and activity is now dwindling from this major source of meteoric activity. The radiant is currently located at 03:40 (055) +59. This position lies in southwestern Camelopardalis, eight degrees north of the second 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. Predawn hourly rates this weekend would be near three as seen from mid-northern latitudes and less than  one as seen from south tropical latitudes. 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.

Another new source found by 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 20 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 03:36 (054) +38, which is actually situated in southeastern Perseus, some six degrees southeast of the famous naked eye eclipsing binary star known as Algol (Beta 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 68 km/sec., the average Alpha Triangulid meteor would be swift. Meteors from this radiant may be associated with a defunct shower known as the Beta Perseids.

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 tropical southern latitudes (25S), morning rates would also be near eight 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 during this period due to bright 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.

Kappa Cygnids (KCG) - 18:28 (277) +58   Velocity - 27km/sec.
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr

Anthelions (ANT) - 22:32 (338) -07  Velocity - 30km/sec.
Northern Hemisphere - 2 per hr.  Southern Hemisphere - 2 per hr

Delta Aquariids (SDA) - 23:52 (358) -11  Velocity - 42km/sec.
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr

IMO #136 - 02:04  (031) +42   Velocity - 46km/sec.
Northern Hemisphere - <1 per hr.   Southern Hemisphere - <1 per hr

Perseids (PER) 03:40 (055) +59  Velocity - 61km/sec.
Northern Hemisphere - 3 per hr.  Southern Hemisphere - <1 per hr

Alpha Triangulids (ATR) -03:36 (054) +38  Velocity - 68km/sec.
Northern Hemisphere - <1 per hr. Southern Hemisphere - <1 per hr

Clear Skies!
Robert Lunsford
American Meteor Society