Meteor Activity Outlook for August 1-7, 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 full phase on Thursday August 6th. This weekend and early next week there is a window of opportunity to view the meteor activity during the dark period between moonset and dawn. This is especially true for observers viewing from the northern hemisphere as the moon currently lies well south of the ecliptic. As Wednesday arrives the full moon is in the sky nearly the entire night. The estimated total hourly rates for evening observers this week is near four no matter your location. For morning observers the estimated total hourly rates should be near twenty seven for those located in the mid-northern hemisphere (45 N) and twenty five for those viewing from the mid-southern hemisphere (45 S). 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 August 1/2. 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 18:52 (283) +58. This position is located in southern Draco, four 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 20:40 (310) -8. This position lies in western Aquarius, three degrees northwest of the fourth magnitude star Epsilon Aquarii. 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 would be near two per hour no matter your location. Don't confuse these meteors with the nearby 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 24 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 21:24 (321) -13. This area of the sky lies in northeastern Capricornus, five degrees northwest of the third magnitude star Delta Capricornii. Actually any meteor from eastern Capricornus as well as western Aquarius, 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.

The Delta Aquariids (SDA) are active from a radiant at 22:48 (342) -15. This position lies in southwestern Aquarius, very close to the third magnitude star Delta Aquarii. The radiant is best placed near 0300 LDT, when it lies highest in the sky. Current rates would be lie between five and ten shower members per hour, depending on your latitude. With an entry velocity of 43 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.

The Piscis Austrinids (PAU) is a weak shower with a radiant is located at 23:00 (345) -28. This area of the sky lies in western Piscis Austrinus, just northeast of the bright star Fomalhaut (Alpha Piscis Austrini). These meteors are best seen near 0300 LDT, when the radiant lies highest above the horizon. One can expect rates near one per hour from the southern hemisphere and less than one from the north. At 35/km per second, these meteors are of average velocity, slower than the Aquariids but faster than the Alpha Caps and the antihelion meteors.

Perseid (PER) activity is now near five per hour as seen from the northern hemisphere. These rates will increase gradually as we approach the peak on the morning of August 12. The current radiant position lies at 02:12 (033) +55, which is located in extreme northwestern Perseus, just three degrees south of the famous "Double Cluster". The nearest easily seen star is Eta Persei which lies six degrees to the northeast. 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. 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 twelve 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 eleven 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. Evening rates reduced due to moonlight.

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