Meteor Activity Outlook for July 26-August 1, 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 new phase on Friday August 1st. At that time the moon will be located near the sun and will not be visible in the night sky. This weekend the waning crescent moon will light the morning skies but successful observations may still be obtained by facing in a direction so that the moon is out of your field of view. As seen from the mid-northern hemisphere (45 N) the estimated total hourly rates during the evening observers would be near three. For morning observers the estimated total hourly rates should be near twenty five. For those located in the mid-southern hemisphere (45 S) morning rates would be near thirty 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. Morning rates are reduced due to moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning July 26/27. 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 20:20 (305) -11. This position lies in northwestern Capricornus, two degrees north of the third magnitude double star Alpha Capricornii. 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 for those in the northern hemisphere and three as seen from the southern hemisphere. Don't confuse 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, 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 21:08 (317) -15. This area of the sky lies in northern Capricornus, two degrees north of the third magnitude star Theta Capricornii. Actually any meteor from 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) reach maximum activity on Sunday July 27th from a radiant located at 22:36 (339) -16. This position lies in southwestern Aquarius, three degrees west of the third magnitude star Delta Aquarii. The radiant is best placed near 0300 LDT, when it lies highest in the sky. Current rates would range from ten to fifteen shower members per hour, depending on your latitude. The optimal latitudes for viewing this shower lie in the southern tropics where the radiant passes overhead. 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. The moon may affect rates more than usual for this shower.

The Pisces Austrinids (PAU) is a weak shower with a radiant is located at 22:44 (341) -30. This area of the sky lies in western Piscis Austrinus, five degrees west 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 three per hour from the southern hemisphere and near two 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 three 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 01:40 (025) +53, which is located in extreme northwestern Perseus. The nearest easily seen star is fourth magnitude 51 Andromedae, lying five degrees to the south of the Perseid radiant. 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 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.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are finally beginning to increase. One would expect to see approximately eight 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 nine 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 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.

SHOWER DATE OF MAXIMUM ACTIVITY CELESTIAL POSITION ENTRY VELOCITY CULMINATION HOURLY RATE CLASS*
    RA (RA in Deg.) DEC Km/Sec Local Daylight Time North-South  
             
Alpha Capricornids (CAP) Jul 30 20:20 (305) -11 23 01:00 2 - 3 II
Antihelion (ANT) - 20:20 (305) -11 30 02:00 2 – 3 II
Delta Aquariids (SDA) July 27 21:48 (327) -19 41 03:00 10 – 15 I
Pisces Austrinids (PAU) July 27 22:44 (341) -30 35 03:00 2 - 3 II
Perseid (PER) August 12 01:40 (025) +53 59 06:00 3 - <1 II