(meteorobs) Meteor Activity Outlook for July 21-27, 2012

[Robert Lunsford]

During this period the moon reaches its first quarter phase on Wednesday the 25th. At this time the moon will be located ninety degrees east of the sun and set near midnight local daylight time (LDT). This weekend the waxing crescent moon will set during the late evening hours and will not hamper observing efforts during the more active morning hours. The estimated total hourly meteor rates for evening observers this week is near four no matter your location. For morning observers the estimated total hourly rates should be near sixteen from the mid-northern hemisphere and fourteen 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.

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 21/22. 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:

A new source found by the IMO video cameras to be active this time of year are the July Zeta Draconids (ZED). This radiant has been found to be active from July 19-29. Maximum activity activity occurs on the 19th from a position of  17:23 (263) +61, which is situated in southern Draco, five degrees southeast of the third magnitude star Al dhibain (Zeta Draconis). Due to a low amount of data the mean position of activity shifts quite a bit night to night so consider this a wide radiant until better parameters can be obtained. Current rates would most likely be less than one per hour no matter your location. The radiant is best placed near 2200 (10pm) LDT when it lie highest above the horizon. With an entry velocity of 23 km/sec., the average July Zeta Draconid meteor would be slow.

The Alpha Capricornids (CAP) are active from a wide radiant located at 20:04 (301) -12. This position lies near the Sagittarius, Aquila, Capricornus border, three 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 no matter your location. 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 large Antihelion (ANT) radiant is currently located at 20:48 (312) -17. This position lies in central Capricornus, four degrees west of the fourth  magnitude star Dorsum (Theta Capricorni). Due to the large size of this radiant, Antihelion activity may also appear from southern Aquila, Microscopium, eastern Sagittarius, northwestern Aquarius,  and western Piscis Austrinus as well as Capricornus. 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 near their lowest of the year with one per hour no matter your location . With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

Activity from the Delta Aquariids (SDA) will begin this weekend from a radiant located at 22:18 (334) -18. This position is located in southwestern Aquarius, eight degrees southwest of the third magnitude Delta Aquarii. Maximum activity is expected on July 29th. Hourly rates will depend on your latitude. Those viewing from the southern tropics will see the best rates of near 1-2 per hour. Rates seen from mid-northern latitudes will range from 0-1 per hour, depending on the haziness of your skies. 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 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 22:23 (336) -32. This position lies in central Piscis Austrinus, eight degrees southwest of 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.

The July Pegasids (JPE) are active with low rates during most of July with maximum activity occurring on the 10th. The radiant is currently located at 23:52 (358) +14. This area of the sky lies in southeastern Pegasus, four degrees west of the third magnitude star Algenib (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 per hour 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 01:04 (016) +52. This position lies in southern Cassiopeia, six degrees southeast 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. Since the maximum is not until August 12th, current rates would be only two to three 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 source found by the IMO video cameras to be active this time of year is the Phi Piscids (PPS). This radiant has been found to be active from June 14 through July 30 with maximum activity occurring on July 1st. Current rates would most likely be less than one per hour no matter your location.  The radiant is currently located at 01:56 (029) +36, which is situated on the Andromeda/Triangulum border, three degrees northwest of the third magnitude star Beta Triangulum. The radiant rises near midnight LDT but does not reach a sufficient altitude above the horizon until three hours later. Activity would best seen during the last dark hour of the morning when the radiant is located highest in a dark sky. With an entry velocity of 71 km/sec., the average Pi Piscid 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 three per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near eight 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 .

July Zeta Draconids (ZED) - 17:23 (263) +61   Velocity 23km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Alpha Capricornids (CAP) - 20:04 (301) -12   Velocity 25km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 1 per hour

Antihelions (ANT) - 20:48 (312) -17   Velocity 30km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 1 per hour

Delta Aquariids (SDA) - 22:18 (334) -18   Velocity 42km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 2 per hour

July Pegasids (JPE) - 23:52 (358) +14   Velocity 68km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Perseids (PER) - 01:04 (016) +52   Velocity 61km/sec
Northern Hemisphere - 3 per hr   Southern Hemisphere - 1 per hour

Phi Piscids (PPS) - 01:56 (029) +36   Velocity 71km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society