Meteor Activity Outlook for July 25-31, 2009

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 first quarter phase on Tuesday July 28th. At this time the moon will be located ninety degrees east of the sun and will set near 0100 local daylight time (LDT). This weekend the waxing crescent moon will set long before the prime morning observing hours arrive. 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 four for those located in the mid-northern hemisphere (45 N) and twenty eight 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 July 25/26. 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 20:16 (304) -11. This position lies in extreme northwestern Capricornus, just two degrees north 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. With maximum activity occurring on the 28th, current rates would be near two per hour, no matter your location. 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 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 21:04 (316) -15. This area of the sky lies in central Capricornus, two degrees north of the fourth magnitude start Theta Capricornii. Actually any meteor from Capricornus, southeastern Aquila, 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 the 30th with ZHR's near twenty. You will not see twenty per hour unless you are watching from dark tropical areas where the radiant approaches the zenith. More likely, you will see ten shower members per hour, depending on your latitude and the hour of the night. The radiant is located at 22:28 (337) -17. This position lies in southwestern Aquarius, seven degrees west of the third magnitude star Delta Aquarii. The radiant is best placed near 0300 LDT, when it lies highest in the sky. With an entry velocity of 43 km/sec., most activity from this radiant would be of average speed. These meteors tend to be faint so the darkest skies are necessary in order to see this shower well.

The Pisces Austrinids (PAU) is a weak shower with a radiant is located at 22:36 (339) -31. This area of the sky lies in central Piscis Austrinus, eight degrees southwest 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 two per hour from the southern hemisphere and one from the north. At 35/km per second, these meteors are of average velocity, slower than the Delta Aquariids but faster than the Alpha Caps and the antihelion meteors.

The Perseids (PER) are now active from a radiant located at 01:32 (023) +53. This position lies on the Cassiopeia/Perseus border, four degrees southeast of the fourth magnitude star Theta Cassiopeiae. The radiant is best placed during the last hour before the start of morning twilight when it lies highest in a dark sky. Current rates would be near three per hour, as seen from the northern hemisphere. Activity from this source is not visible south of 40 degrees south latitude. With an entry velocity of 59 km/sec., most activity from this radiant would be swift.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately eleven Sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near three per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near thirteen 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. Evening rates are reduced by 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.