Meteor Activity Outlook for July 30-August 5, 2011

During this period the moon reaches its new phase on Saturday July 30th. At this time the moon will lie near the sun and will not be visible at night. Next week the waxing crescent moon will enter the evening sky but will not cause any interference to observers as it will set long before the active morning hours arrive. This period will be the best time to view meteor activity during July and August as the Perseids will suffer from a full moon at the time of their maximum.  The estimated total hourly rates for evening observers this week is near six as seen from the northern hemisphere and seven as seen from the southern hemisphere. For morning observers the estimated total hourly rates should be near thirty no matter your location. 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 July 30/31. 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:

The Alpha Capricornids (CAP) are active from a wide radiant located at 20:22 (306) -10. This position lies in northwestern Capricornus, two degrees north 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. Current rates should be near two per hour as seen from the northern hemisphere and three per hour from the southern. Maximum activity occurs on July 30th. 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 21:20 (320) -14. This area of the sky lies on the border of  Capricornus and Aquarius, three degrees north of the fourth magnitude star Iota 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, western Aquarius, eastern Aquila, or northern Microscopium 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) will reach maximum activity on Saturday July 30th. Hourly rates will depend on your latitude. Those viewing from the southern tropics will see the highest rates of near 15 per hour. Rates seen from mid-northern latitudes will range from 5-10 per hour, depending on the haziness of your skies.  The radiant is currently located at 22:45 (341) -16. This position lies in southwestern Aquarius, two degrees west of the third magnitude star Delta Aquarii. The radiant rises near 2200 (10pm) LDT for observers located in the mid northern latitudes, but 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 22:56 (344) -29. This position lies in eastern Piscis Austrinus, very close to the bright 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 00:30 (008) +18. This area of the sky lies in north-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 01:58 (029) +54. This position lies in western Perseus, twelve degrees north of the famous second magnitude double star Almach (Gamma Andromedae). The radiant also forms an equilateral triangle with Almach and 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 3-5 per hour at best, as seen from the northern hemisphere. Activity from this source is poorly seen from the southern hemisphere and not visible at all south of 40 degrees south latitude. This shower does not peak until August 13, and the bright moon will spoil the show. With an entry velocity of 61 km/sec., most activity from this radiant 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 three 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 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.

Tags: 2011 Major Annual Meteor Showers 2011 Meteor Showers 2011 Perseids Alpha Capricornids Alpha Caps Antihelion meteors August Piscids Delta Aquariids July Meteor Showers July Pegasids Perseids Piscis Austrinids South Delta Aquariids

Robert Lunsford

Bob has been interested in the stars as far back as he can recall His first experience with meteors was a biggie, the 1966 Leonid shower. In 1980, a major awaking occurred. He received a sample copy of Meteor News. He was amazed to learn there was a group actually devoted strictly to meteor observing! He joined the group also started to view some of the minor showers list among the pages of Meteor News. Lastly, he was contracted by Springer Publishing in 2007 to write a book on observing meteors. The book is now available and hopefully will be a useful guide to all interested in the enjoyable field of meteor observing.