Meteor Activity Outlook for August 10-16, 2007

August is the best month for viewing meteor activity from the northern hemisphere. Not only is the activity enjoyable but the balmy nights are much more pleasant than those experienced later in the year. As the month begins the southern radiants are still active and often matching the sporadic rates. The sporadic rates increase as the month progresses providing a decent show for the normally slow evening hours. The Perseids kick into high gear the second week of the month and fill the skies with colorful streaks of light during the entire night. From the southern hemisphere activity falls precipitously. This is much like what the northern hemisphere experiences moving from January into February. The southern radiants put on a good show the first week of the month. They taper off the second week and are nearly extinct by the third. In the meantime the sporadic rates that were so impressive in early July are now half as strong and still getting weaker. Unless you are located near the equator you will not see much of the Perseids. From the southern hemisphere any evening Perseids are impossible to see. You have to wait until the last hours before dawn and hope that some will shoot upwards from low in the northern sky.

During this period the moon reaches its new phase on Sunday August 12. At this time the moon is located near the sun and is invisible at night. Late in the period the waxing crescent moon will enter the evening sky but will not interfere with meteor observing. The estimated total hourly rates for evening observers this week is near four for those located north of the equator and two for observers south of the equator. For morning observers the estimated total hourly rates should be near fifty-five for those located in the northern hemisphere and twenty for those viewing from south of the equator. 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.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning August 11/12. 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. Doing this 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 Kappa Cygnids (KCG) are active from a wide radiant located at 18:52 (284) +58. This position is located in southern Draco, three degrees northwest of the fourth magnitude star Kappa Cygni. Current rates would be near one shower member per hour. With an entry velocity of 25 km/sec. most of these meteors will appear to travel slower than average. The radiant is best placed near 2300 Local Daylight Time (11pm LDT) when it lies nearly overhead for much of the Northern Hemisphere. Due to its high northern declination this activity is not well seen from the Southern Hemisphere.

The Alpha Capricornids (CAP) are active from a wide radiant located at 21:20 (320) -05. This position lies in western Aquarius, two degrees northwest of the third magnitude star Sadalsuud (Beta Aquarii). The radiant is best placed near 0100 local daylight time, when it lies highest in the sky. Current rates would be less than one per hour, no matter your location. Don't mix 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 23 km/sec., most activity from this radiant would be slow.

The Antihelion (ANT) radiant is now centered at 22:08 (332) -09. This area of the sky is located in a southwestern Aquarius, two degrees southwest of the fourth magnitude star Theta Aquarii. 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 per hour regardless of your location. With an entry velocity of 30 km/sec., the average antihelion meteor would be of medium-slow speed.

The Delta Aquariids (SDA) are active from a radiant located at 23:20 (350) -13. This position lies in eastern Aquarius, close to the fourth magnitude star Omega Aquarii. The radiant is best placed near 0300 local daylight time, when it lies highest in the sky. Current rates would be near two per hour visible from the southern hemisphere and one per hour from the northern hemisphere. With an entry velocity of 41 km/sec., most activity from this radiant would be of average velocities.

The Perseids (PER) reach maximum activity on August 13 with average rates expected to be near sixty shower members per hour. The current radiant position lies at 03:04 (046) +58, which is located where the borders of Perseus, Cassiopeia, and Camelopardalis meet. This position is also three degrees northwest of the fourth magnitude star Eta Persei. While the radiant lies above the horizon for most observers in the northern hemisphere, it is best placed during the last few hours before dawn. Due to the high northern declination (celestial latitude) of the radiant, rates seen from the Southern Hemisphere are very low when compared to those seen north of the equator. At 59 km/sec., Perseid meteors are swift, often exhibiting persistent trains.

Sporadic rates are now rising for observers in the northern hemisphere and falling steadily for those located south of the equator. One would expect to see perhaps twelve random meteors during the last hour before dawn from rural observing sites in the northern hemisphere. During the first dark hour after the end of evening twilight, perhaps three random meteors can be seen per hour. Sporadic rates increase as the night progresses so rates seen near midnight would be near six per hour. As seen from the southern hemisphere late morning rates would now be near ten per hour. During the first dark hour after the end of evening twilight, perhaps two random meteors can be seen per hour, increasing to five by midnight.