Meteor Activity Outlook for July 12-18, 2008

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 full phase on Friday July 18th. At that time the moon will be located 180 degrees from of the sun and will be in the sky all night long. This weekend successful observations may be obtained between the time of moonset and dawn. The window of darkness shrinks until July 17, when it essentialy reached zero. As seen from the mid-northern hemisphere (45 N) the estimated total hourly rates during the evening observers would be near two. For morning observers the estimated total hourly rates should be near twelve. For those located in the mid-southern hemisphere (45 S) morning rates would be near twenty and evening rates near three. Locations between these two extremes would see activity between the listed figures. These rates assume that you are watching from rural areas away from all sources of light pollution. 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. Evening rates are reduced due to moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning July 12/13. 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:

The Alpha Capricornids (CAP) are active from a wide radiant located at 19:28 (292) -14. This position lies in northeastern Sagittarius, a dozen degrees west of the third magnitude double star alpha Capricornii. The radiant is best placed near 0100 LDT, when it lies on the meridian and is highest in the sky. Current rates would be less than one per hour, no matter your location. 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 23 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 now centered at 20:12 (303) -18. This area of the sky lies in western Capricornus, three degrees southwest of the third magnitude star beta Capricornii. Actually any meteor from western Capricornus, southwestern Aquila, as well as eastern Sagittarius could be a candidate for this shower. This radiant is best placed near 0200 LDT when it lies on the meridian and is highest in the sky. Rates at this time should be near two for northern observers and three for observers south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.

Sirko Molau's study of video radiants has revealed activity during the period July 8-22, from an area in northwestern Aquarius. The first of two maximums occured on July 10 with the radiant located at 21:00 (315) -04. This position lies five degrees northwest of the third magnitude star Sadalsuud (Beta Aquarii). This radiant is best placed near 0300 LDT when it lies highest in the sky. Rates would most likely be less than one shower member per hour no matter your location. At 40km/sec., the average meteor from this radiant would be of medium velocity.

The Delta Aquariids (SDA) are active from a radiant located at 21:48 (327) -19. This position lies in eastern Capricornus, two degrees south of the third magnitude star Nashira (delta Capricornii). The radiant is best placed near 0300 local daylight time, when it lies highest in the sky. Current rates would be low, less than one shower member per hour. With an entry velocity of 41 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. This shower peaks on July 27th with expected ZHR's near twenty.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are finally beginning to increase. One would expect to see approximately nine random meteors during the last hour before dawn from rural observing sites and two per hour during the evening hours. As seen from the mid-southern hemisphere (45S) morning rates would be near seventeen per hour as seen from rural observing sites and four per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Evening 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.