(meteorobs) Meteor Activity Outlook for August 11-17, 2012

[Robert Lunsford]

During this period the moon reaches its new phase on Friday August 17th. At this time the moon will be located near the sun and will not be visible at night. This weekend the waning crescent moon will rise during the early morning hours, giving off some glare in the eastern sky. You can compensate for this by facing away from the moon in another direction where the sky should be largely unspoiled by moonlight. The estimated total hourly meteor rates for evening observers this week is near six 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 sixty from the mid-northern hemisphere and twenty 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. Morning rates are slightly reduced 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 11/12. 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 19:00 (285) +51. This position lies on the Cygnus/Draco border, eight degrees northwest of the third magnitude star Rukh (Delta Cygni). Maximum activity occurs on August 17th so current rates would be one 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 22:08 (332) -09. This position lies in central Aquarius, two degrees southwest of the fourth magnitude star Theta Aquarii. Due to the large size of this radiant, Antihelion activity may also appear from eastern Capricornus, western Pisces, and southwestern Pegasus 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 as seen from the northern hemisphere and three per hour as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

The Delta Aquariids (SDA) are still active from a radiant located at 23:28 (352) -13. This position is located in east-central Aquarius, four degrees southeast of the naked eye triple star known as Psi Aquarii. Current hourly rates would be one from the northern hemisphere and two 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.

The Eta Eridanids (ERI) are active from July 24 through August 18 with maximum activity occurring on August 8. The current radiant position is 03:00 (045) -10, which places it in western Eridanus, just one degree southeast of the fourth magnitude star Eta Eridani. Current rates would be near one per hour no matter your location. The radiant is best placed during the last hour before dawn, when it lies highest in a dark sky. With an entry velocity of 66 km/sec., the average Eta Eridanid meteor would be swift.

The Perseids (PER) peak on Sunday morning from a radiant located at 03:12 (048) +58. This position lies near the intersection of Cassiopeia, Perseus, and Camelopardalis. Gamma Persei lies four degrees to the southwest of the radiant. The radiant is circumpolar north of 32 degrees north latitude but best placed during the last hour before the start of morning twilight, when it lies highest in a dark sky. Expected maximum rates, when the radiant is located highest in a dark sky, are near forty per hour as seen from the northern hemisphere and ten per hour as seen from tropical southern latitudes. Rates are slightly reduced due to moonlight, as the 25 percent illuminated moon lies fairly close to the radiant. Activity from this source is not visible south of 35 degrees south latitude. With an entry velocity of 61 km/sec., most activity from this radiant would be swift. For more information on how to watch for Perseid meteors, see the article at: Viewing the 2012 Perseid Meteor Shower

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 03:16 (049) +37, which is actually situated in southern Perseus, five degrees southeast of the famous variable 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 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 twelve sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near four per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near six 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. Morning rates are slightly reduced due to moonlight.

The list below presents a summary of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning August 11/12, but may be used all week. 

Kappa Cygnids (KCG) - 19:00 (285) +51   Velocity 23km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - <1 per hour

Antihelions (ANT) - 22:08 (332) -09   Velocity 30km/sec
Northern Hemisphere - 2 per hr   Southern Hemisphere - 3 per hour

Delta Aquariids (SDA) - 23:28 (352) -13   Velocity 42km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 2 per hour

Eta Eridanids (ERI) - 03:00 (045) -10   Velocity 66km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 1 per hour

Perseids (PER) - 03:12 (048) +58   Velocity 61km/sec
Northern Hemisphere - 40 per hr  Southern Hemisphere - 10 per hour

Alpha Triangulids (ATR) - 03:16 (049) +37   Velocity 67km/sec
Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society