Meteor Activity Outlook for August 22-28, 2009

Meteor activity kicks into high gear in August as seen from the northern hemisphere. The main reason for all this activity is the Perseid shower that peaks on August 12. This shower is active most of the month and remains above the level of the sporadic background for a week centered on August 12. The sporadic activity is also increasing as seen from the northern hemisphere and is now nearly double the rates from just three months ago. As seen from south of the equator, meteor rates are still decent but falling rapidly. The sporadic rates seen at the beginning of the month will be twice as much as those seen during the last days of the month. The Perseid radiant does not rise high into the sky as seen in the southern hemisphere so rates from this shower are greatly reduced when compared to the northern hemisphere.

During this period the moon reaches its first quarter phase on Thursday August 27th. At that time the moon will set near 0100 local daylight time LDT and will allow unhampered observing during the busy morning hours. This weekend the waxing crescent moon will set shortly after the end of evening twilight and will not be a factor at all. The estimated total hourly rates for evening observers this week is near four as seen from the northern hemisphere and three from the southern hemisphere. For morning observers the estimated total hourly rates should be near twenty from the northern hemisphere and twelve as seen from the 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 positions and rates listed below are exact for Saturday night/Sunday morning August 22/23. 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 Kappa Cygnids (KCG) are active from a wide radiant located at 19:08 (287) +60. This position is located in southern Draco, six degrees north 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 large Antihelion (ANT) radiant is now centered at 22:52 (343) -06. This area of the sky lies in northeastern Aquarius, ten degrees north of the third magnitude star Delta Aquarii. Actually any meteor from Aquarius, eastern Capricornus, as well as western Pisces, 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 three no matter 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 still active from a radiant at 23:56 (359) -10. This position lies on the Aquarius/Cetus border, fifteen degrees northeast of the third magnitude star Delta Aquarii. The radiant is best placed near 0300 LDT, when it lies highest in the sky. Current hourly rates would be less than one from the northern hemisphere and one as seen from south of the equator. With an entry velocity of 43 km/sec., most activity from this radiant would be of average velocities.

The Perseids (PER) peaked on August 12th with good rates despite the unfavorable lunar conditions. The current radiant position lies at 04:00 (060) +58, which is located in southern Camelopardalis, ten degrees north of the second magnitude star Mirfak (Alpha Persei). The radiant is well placed for those in the northern hemisphere during the last few hours before dawn. Due to the high northern declination (celestial latitude) of the radiant, rates witnessed from the southern hemisphere are very low when compared to those seen north of the equator. Current hourly rates would be two from the northern hemisphere and less than one as seen from south of the equator. At 59 km/sec., Perseid meteors are swift, often exhibiting persistent trains.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are becoming more active. One would expect to see approximately thirteen random meteors during the last hour before dawn from rural observing sites and three per hour during the evening hours. As seen from the mid-southern hemisphere (45S) morning rates would be near eight per hour as seen from rural observing sites and two per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.

The table below presents a summary of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning August 22/23, but may be used all week.