(meteorobs) Meteor Activity Outlook for July 14-20, 2012

[Robert Lunsford]

During this period the moon reaches its new phase on Wednesday the 18th. At this time the moon will be located near the sun and will be invisible at night. This will be the best time of the month to try and view meteor activity as the bright moon will spoil the showers that peak near months end. This weekend the waning crescent moon will rise during the late morning hours and will not hamper observing efforts. 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 fourteen 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 14/15. 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:

The Alpha Capricornids (CAP) are active from a wide radiant located at 19:56 (297) -14. This position lies in northeastern Sagittarius, seven 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 less than one per hour as seen from the northern hemisphere and near one 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 large Antihelion (ANT) radiant is currently located at 20:20 (305) -18. This position lies in western Capricornus, three degrees south of the third magnitude star Dabih (Beta Capricorni). Due to the large size of this radiant, Antihelion activity may also appear from southern Aquila, Microscopium, eastern Sagittarius, northwestern Aquarius, western Piscis Austrinus, and Scutum 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 less than one per hour as seen from the northern hemisphere and one per hour as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.

The Sigma Capricornids (SCA) are a new source of activity to look for this time of year. Actually this radiant has been listed before many years ago but had become lost in the many radiants active in this area of the sky this time of year. With over one million meteors available for analysis, the International Meteor Organization's video section, led by Sirko Molau, has been able to isolate activity from this radiant. The radiant has been found to be active from June 19 through July 24 with maximum activity occurring on June 27. In early July it is still one of the most active radiants in the sky. Unfortunately that is not saying much as the strongest radiant only produces two meteors per hour this time of year. This radiant is now located at 21:12 (318) -03. This area of the sky is actually in western Aquarius, four degrees northwest of the third magnitude star Sadalsuud (Beta Aquarii). This radiant is best positioned for view on the meridian near 0300 LDT. With an entry velocity of 42 km/sec., the average Sigma Capricornid meteor would be of medium speed. Meteors from this source should be easy to distinguish from the slower Antihelion meteors as the two sources are separated by nearly twenty degrees. One must have both radiants within your field of view to properly distinguish between the two sources.

Another radiant returning to the list of active radiants are the July Pegasids (JPE). This source is active with low rates during most of July with maximum activity occurring on the 10th. The radiant is currently located at 23:28 (352) +12. This area of the sky lies in northern Pegasus, five degrees east of the third magnitude star Scheat (Beta 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 near 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 now active from a radiant located at 00:25 (006) +50. This position lies in southern Cassiopeia, seven degrees southwest 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 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 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. During late June and early July this radiant is often the most active source of meteors in the sky with 1-2 shower members per hour during the early morning hours. The radiant is currently located at 01:30 (023) +31, which is situated on the Pisces/Triangulum border, four degrees northwest of the third magnitude star Ras al Muthallah (Alpha Triangulum). This position also happens to be very close to the large spiral galaxy M33. 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.

Studies by Sirko Molau and Juergen Rendtel of the IMO's video data has revealed an active radiant located in Andromeda this time of year. The c-Andromedids (CAN) are active from July 4-16, with maximum activity occurring on the 12th. The radiant position is currently located at 02:22 (035) +50. This area of the sky lies in extreme northeastern Andromeda, eight degrees north of the famous second magnitude double star Almach (Gamma Andromedae). 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 59 km/sec., the average c-Andromedid meteor would be of swift speed.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately nine 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 also be near nine 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 .
 
Alpha Capricornids (CAP) - 19:56 (297) -14   Velocity 25km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - 1 per hour

Antihelions (ANT) - 20:20 (305) -18   Velocity 30km/sec
Northern Hemisphere - <1 per hr   Southern Hemisphere - 1 per hour

Sigma Capricornids (SCA) - 21:12 (318) -03   Velocity 42km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 1 per hour

July Pegasids (JPE) - 23:28 (352) +12   Velocity 68km/sec
Northern Hemisphere - 1 per hr   Southern Hemisphere - 1 per hour

Perseids (PER) - 00:25 (006) +50   Velocity 61km/sec
Northern Hemisphere - 2 per hr   Southern Hemisphere - <1 per hour

Phi Piscids (PPS) -01:30 (023) +31   Velocity 71km/sec
Northern Hemisphere - 2 per hr Southern Hemisphere - 1 per hour

c-Andromedids (CAN) - 02:22 (035) +50   Velocity 59km/sec
Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

Clear Skies!
Robert Lunsford
American Meteor Society