The American Meteor Society

Meteor Activity Outlook for 
  July 17-23, 2010

By Robert Lunsford 
AMS Operations Manager

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 first quarter phase on Sunday July 18th. At this time the moon will be located ninety degrees east of the sun and will set near 0100 for those living in mid-northern latitudes. Later next week the waxing gibbous moon will intrude during the later morning hours limiting the dark skies to just before the start of morning twilight. The estimated total hourly rates for evening observers this week is near three for northern observers and four for those viewing from south of the equator. For morning observers the estimated total hourly rates should be near sixteen from the northern hemisphere and twenty three 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.

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 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 showers are expected to be active this week:

Recent studies of the IMO video database by Sirko Molau and Juergen Rendtel have revealed an active radiant in Lyra this time of year. The Mu Lyrids (MUL) are active from July 15th through the 20th with maximum activity occurring on the 18th. The radiant is currently located at 18:12 (273) +39. This area of the sky is located in western Lyra, four degrees west of the brilliant star Vega (Alpha Lyrae). This radiant is best placed near midnight when it lies highest above the horizon. Hourly rates are expected to be less than one. With an entry velocity of 23 km/sec., the average Mu Lyrid meteor would be slow.

The Alpha Capricornids (CAP) are active from a wide radiant located at 19:56 (299) -13. This position lies in northeastern Sagittarius, five degrees west 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 one per hour as seen from the northern hemisphere and two per hour from the southern. Don't confuse these meteors with the more numerous 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 20:32 (308) -17. This area of the sky lies in western Capricornus. The nearest bright star is third magnitude Dabih (Beta Capricornii), which lies some four degrees to the northwest. 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 eastern Sagittarius, Microscopium, Capricornus, western Aquarius, or southeastern Aquila could be a candidate for this shower. Rates at this time should 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 medium-slow speed.

The Delta Aquariids (SDA) become active next week with rates of 1-2 per hour. Next Wednesday, July 21st, the radiant will be located at 22:12 (333) -19. This position lies in southwestern Aquarius, ten degrees 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. Maximum activity occurs on July 30th. With an entry velocity of 43 km/sec., most activity from this radiant would be of average velocities. These meteors tend to be faint so the darkest skies are necessary in order to see this shower well.

Recent studies of the IMO video database by Sirko Molau and Juergen Rendtel have confirmed that the July Pegasids (JPE) are still an active shower. This shower has a much longer activity period than once thought, being active from July 7th through the 29th. Maximum activity occurred on July 10. The radiant currently lies at 23:36 (354) +13. This area of the sky is located in southern Pegasus, seven degrees southeast of the second magnitude star Markab (Alpha Pegasi). This radiant is best placed during the last hour before dawn when it lies highest in a dark sky. Even at maximum activity hourly rates are expected to be less than one. With an entry velocity of 68 km/sec., the average July Pegasid meteor would be swift.

The Perseids (PER) are now active from a radiant located at 00:44 (011) +51. This position lies in southern Cassiopeia, six degrees south of the second magnitude star Shedar (Alpha Cassiopeiae). 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 one to two 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.

Another new shower discovered by Sirko Molau and Juergen Rendtel are the Alpha Triangulids (ATR). This short-lived shower is only active from July 21-26 with maximum activity occurring on the 22th. At maximum, the radiant is located at 01:56 (029) +28. This area of the sky is located in southern Triangulum, only one degree south of the thrid magnitude star Alpha Trianguli. 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 one. With an entry velocity of 71 km/sec., the average Alpha Triangulid meteor would be swift.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately ten 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 fifteen 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.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.

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
Mu Lyrids (MUL)	July 18	18:12 (273) +39	23	00:00	<1 - <1	II
Alpha Capricornids (CAP)	July 28	19:56 (299) -13	25	01:00	1 - 2	II
Antihelion (ANT)	-	20:32 (308) -17	30	02:00	2 - 3	II
Delta Aquariids (SDA)	Jul 30	22:12 (333) -19	43	04:00	1 - 2	I
July Pegasids (JPE)	Jul 10	23:36 (354) +13	68	05:00	<1 - <1	IV
Perseids (PER)	Aug 13	00:44 (011) +51	61	06:00	2 - 1	I
Alpha Triangulids (ATR)	Jul 22	01:56 (029) +28	61	07:00	<1 - <1	IV

*For a detailed explanation on the different classes of meteor showers and other astronomical terms, please visit: http://www.amsmeteors.org/showers.html#X2010

Last updated: July 16, 2010 at 1800 UT