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Meteor Activity Outlook for July 7-13, 2012

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  • Robert Lunsford
    During this period the moon reaches its last quarter phase on Wednesday the 11th. At this time the moon will be located ninety degrees east of the sun and will
    Message 1 of 1 , Jul 7, 2012
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      During this period the moon reaches its last quarter phase on Wednesday the 11th. At this time the moon will be located ninety degrees east of the sun and will rise near midnight local daylight time (LDT) for observers located in mid-northern latitudes. This weekend the waning gibbous moon will rise during the late evening hours and will severely hamper efforts to view meteor activity the remainder of the night. The moonlight situation improves with each passing night it will not be until late in the week when dark skies are available during the early morning hours. The estimated total hourly meteor rates for evening observers this week is near three for observers in the northern hemisphere and four for those south of the equator. For morning observers the estimated total hourly rates should be near ten as seen from mid-northern latitudes and twelve from mid-southern latitudes. 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 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 7/8. 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 large Antihelion (ANT) radiant is currently located at 19:52 (298) -19. This position lies in a blank area of eastern Sagittarius between the third magnitude stars Pi Sagittarii and Dabih (Beta Capricorni). Due to the large size of this radiant, Antihelion activity may also appear from Serpens Cauda, Corona Australis, southern Aquila, Microscopium, western Capricornus, and Scutum as well as Sagittarius. 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 should be 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 21:02 (316) -04. This area of the sky is actually in western Aquarius, five 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 23:08 (345) +11. This area of the sky lies in southern Pegasus, six degrees south of the second magnitude star Markab (Alpha 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.

      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 01:15 (019) +29, which is situated in extreme northeastern Pisces. The nearest bright star is Mirach (Beta Andromedae), which lies seven degrees to the north. 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 01:58 (029) +47. This area of the sky lies in northeastern Andromeda, five 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 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 seven 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 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 unless the
      showers are of short duration. In that case the position on the night of maximum
      activity is listed.

      Antihelions (ANT) - 19:52 (298) -19 Velocity 30km/sec
      Northern Hemisphere - <1 per hr Southern Hemisphere - 1 per hour

      Sigma Capricornids (SCA) - 21:02 (316) -04 Velocity 42km/sec
      Northern Hemisphere - 1 per hr Southern Hemisphere - 1 per hour

      July Pegasids (JPE) - 23:08 (345) +11 Velocity 68km/sec
      Northern Hemisphere - 1 per hr Southern Hemisphere - 1 per hour

      Phi Piscids (PPS) - 01:15 (019) +29 Velocity 71km/sec
      Northern Hemisphere - 2 per hr Southern Hemisphere - 1 per hour

      c-Andromedids (CAN) - 01:58 (029) +47 Velocity 59km/sec
      Northern Hemisphere - <1 per hr Southern Hemisphere - <1 per hour

      Clear Skies!
      Robert Lunsford
      international Meteor Organization
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