[I have been very lax lately in my posting of Bob’s weekly Meteor Activity Outlooks. I’m sorry for that. Here’s this weeks installment and I’ll try to keep up in future weeks.]
The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.
After several months of low activity the meteor rates for both hemispheres see a marked increase in July. In the northern hemisphere the change is not noticeable until mid-month when several southern radiants, the Perseids, and sporadic rates all increase in activity. Southern rates are good all month long.
During this period the moon reaches its last quarter phase on Tuesday August 3rd. At this time the moon will be located 90 degrees west of the sun and will rise near 0100 local daylight time (LDT) for those located in the mid-northern latitudes. This weekend the waning gibbous moon will be in the sky most of the night making it difficult to view any meteor activity. As the moon passes its last quarter phase the situation improves as long as one observes with the the moon far from their field of view. The estimated total hourly rates for evening observers this week is ~4 no matter your location. For morning observers the estimated total hourly rates should be ~17 from the northern hemisphere and ~21 as seen from the 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. During this period, moonlight reduces activity seen during the morning hours.
The radiant positions and rates listed below are exact for Saturday night/Sunday morning July 31/August 1. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.
The following showers are expected to be active this week:
Alpha Capricornids (CAP)
The Alpha Capricornids (CAP) are active from a wide radiant located at 20:30 (307) -09. This position lies in northwestern Capricornus, two 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. Current rates should be ~2 per hour as seen from the northern hemisphere and ~3 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 21:24 (321) -13. This area of the sky lies in northern Capricornus. The nearest bright star is fourth magnitude Iota Capricornii, which lies three degrees to the southwest. This radiant is best placed near 0200 local daylight time (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 northwestern Piscis Austrinus, Microscopium, Capricornus, western Aquarius, or southeastern Aquila could be a candidate for this shower. Rates at this time should be ~2 per hour as seen from the northern hemisphere and ~3 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.
Delta Aquariids (SDA)
The Delta Aquariids (SDA) reach maximum activity on Friday July 30th. Unfortunately the bright moon will obscure most of the activity from this shower. The radiant is located at 22:48 (342) -16. This position lies in southwestern Aquarius, just west of the third magnitude star Delta Aquarii. The radiant is best placed near 0300 LDT, when it lies highest in the sky. The optimal latitudes for viewing this shower lie in the southern tropics where the radiant passes overhead. With an entry velocity of 42 km/sec., most activity from this radiant would be of average velocities.
August Piscids (AUP)
A new shower discovered by Sirko Molau and Juergen Rendtel from the IMO’s video database are the August Piscids (AUP). This shower is only active on eight nights from August 2-9 with maximum activity occurring on the
4th. At maximum, the radiant is located at 00:30 (008) +18. This area of the sky is located in western Pisces, four degrees northwest of the third magnitude star Algenib (Gamma Pegasi). This position is also suspiciously close (15 degrees east) to the radiant of the 1970’s radiant known as the Upsilon Pegasids. Little has been reported of this radiant recently. This radiant is best placed during the last hour before dawn when it lies highest in a dark sky. Hourly rates are expected to be less than 1. With an entry velocity of 66 km/sec., the average August Piscid meteor would be swift.
The Perseids (PER) are active from a radiant located at 02:03 (031) +55. This position lies in western Perseus, twelve degrees north of the famous second magnitude double star Almach (Gamma Andromedae). 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 2-3 per hour at best, as seen from the northern hemisphere. 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.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately five 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 fourteen per hour as seen from rural observing sites and three 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 condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.
Shower Name RA DEC Vel Rates km/s NH SH CAP Alpha Capricornids 20h 30m -09 25 2 3 ANT Antihelions 21h 00m -15 30 2 3 SDA Delta Aquariids 22h 48m -16 42 3 5 AUP August Piscids 00h 30m +18 66 <1 <1 PER Perseids 00h 44m +51 61 3 2 RA - Right Ascension DEC - Declination Vel - Velocity relative to Earth (in km per sec) Rates - Rate of visible meteors per hour from a dark site NH - Northern Hemisphere SH - Southern Hemisphere