Meteor Activity Outlook for July 23-29, 2011

During this period the moon reaches its last quarter phase on Saturday July 23rd. At this time the moon will lie ninety degrees west of the sun and will rise near 0100 local daylight time (LDT) for observers located in the mid-northern latitudes. This situation is not perfect as the bright moon will obscure some of the fainter meteors. Successful meteor watching can be accomplished by viewing in a direction that places the moon far from your field of view. The situation improves as the week progresses as the moon rises later each night and also becomes thinner and less bright. The estimated total hourly rates for evening observers this week is near four as seen from the northern hemisphere and three as seen from the southern hemisphere. For morning observers the estimated total hourly rates should be near fourteen from the northern hemisphere and fifteen as seen from south of the equator. 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 reduced this week 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 July 23/24. 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:

Studies by Sirko Molau and Juergen Rendtel of the IMO’s video data has revealed two active radiants in the constellation of Draco this time of year. The first of these are the Zeta Draconids (ZDR), which are active from July 24-28, with maximum activity occurring on the 24th. The radiant position is currently located at 17:28 (262) +68. This area of the sky lies in eastern Draco, four degrees northeast of the fourth magnitude star Zeta Draconis. A more convenient signpost would be the “Lozenge” or head of Draco, which lies ten degrees to the south.  This radiant is best placed near 2200 (10pm) local daylight time. Rates at this time should be less than one no matter your location. With an entry velocity of 25 km/sec., the average Zeta Draconid meteor would be of slow velocity.

The second radiant currently active in Draco is known as the Gamma Draconids (GDR). This radiant is active from July 23 through the 29th with maximum activity occurring on the 28th. The radiant is currently located at 18:48 (282) +50, which places it in extreme southeastern Draco, ten degrees east of the second magnitude star Eltanin (Gamma Draconis).This radiant is best placed near 2300 (11pm) local daylight time. Rates at this time should be less than one no matter your location. With an entry velocity of 27 km/sec., the average Gamma Draconid meteor would be of slow velocity.

The Alpha Capricornids (CAP) are active from a wide radiant located at 20:08 (302) -12. This position lies where the borders of the constellations of Capricornus, Sagittarius, and Aquila meet. The third magnitude double star Alpha Capricornii lies two degrees to the southeast. 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 20:56 (314) -15. This area of the sky lies in central Capricornus, three degrees northwest of the fourth magnitude star Theta 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, Aquarius, eastern Aquila, eastern Sagittarius, 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) are now active and will reach maximum activity on Saturday July 30th. Rates will be low this weekend but activity will increase next week as the date of maximum activity approaches. The radiant is currently located at 22:20 (335) -18. This position lies in southwestern Aquarius, seven 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. 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 occurs 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 22:30 (338) -31. This position lies in southwestern Aquarius, seven 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. With an entry velocity of 35km/sec., most activity from this radiant would be of average velocities..

Thanks to studies by Sirko Molau and Juergen Rendtel of the IMO’s video data, the July Pegasids (JPE) have returned to the ranks of an active shower. Recent visual observations of these meteors have been scarce to the point of having the shower removed from the IMO’s list. Video data shows a much longer activity period than previously thought, July 7 through the 29th with maximum occurring on the 10th. The radiant position is also further east than previously thought. It is currently located at 23:58 (359) +14. This area of the sky lies in southeastern Pegasus, three degrees west of the third magnitude star Gamma Pegasi. 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 68 km/sec., the average July Pegasid meteor would be of swift speed.

The Perseids (PER) are active from a radiant located at 01:17 (019) +53. This position lies in southern Cassiopeia, five degrees southeast of the second magnitude star Schedar (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 poorly seen from the southern hemisphere and not visible at all south of 40 degrees south latitude. With an entry velocity of 61 km/sec., most activity from this radiant would be swift.

Studies by Sirko Molau and Juergen Rendtel of the IMO’s video data have revealed an active radiant in the constellations of Triangulum and Aries this time of year. The Alpha Triangulids (ATR) are active from July 21 through 26 with maximum activity occurring on the 22nd. The radiant is currently located at 01:54 (029) +24. This area of the sky lies in western Aries, only two degrees west of the second magnitude star Hamal (Alpha Arietis). 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 71 km/sec., the average Alpha Triangulid meteor would be of swift speed.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately seven 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 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 reduced due to moonlight.

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 Alpha Triangulids Antihelion meteors Delta Aquariids Gamma Draconids July Meteor Showers July Pegasids Perseids Piscis Austrinids South Delta Aquariids Zeta Draconids

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.