Meteor Activity Outlook for May 2-8, 2008

May is a fairly slow month for meteor activity. The Eta Aquariids are very active the first week of the month then fade as the month progresses. The only other showers active this month are the Eta Lyrids and the Antihelion radiant. These will add only 1-2 meteors per hour to the total count. Sporadic rates are low but steady as seen from the mid-northern hemisphere (45 N). Sporadic rates seen from the mid-southern hemisphere (45 S) continue to rise this month toward a maximum in July.

During this period the moon reaches its new phase on Monday May 5th. At this time the moon will be located near the sun and will not be visible at night. As seen from the mid-northern hemisphere (45 N) the estimated total hourly rates during the evening observers would be only one. For morning observers the estimated total hourly rates should be near twenty. For those located in the mid-southern hemisphere (45 S) morning rates would be near twenty six and evening rates near two. 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 May 3/4. 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 large Antihelion (ANT) radiant is now centered at 15:44 (236) -20. This area of the sky lies in eastern Libra, five degrees west of the 3rd magnitude star Acrab (Beta Scorpii). Actually any meteor from northwestern Scorpius, southern Ophiuchus, as well as Libra could be a candidate for this shower. This radiant is best placed near 0200 LDT time when it lies on the meridian and is highest in the sky. Rates at this time should be near one for northern observers and two 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 Eta Lyrids (ELY) are produced by comet IRAS-Araki-Alcock, which passed very close to the Earth twenty five years ago this May. Weak activity from this radiant has been seen in most years from May 3 through May 12, with maximum activity occurring on May 8. The current radiant position is located at 18:48 (282) +44. This area of the sky is located in northern Lyra, five degrees northeast of the zero magnitude star Vega (Alpha Lyrae). The best time to view this activity is just before the start of morning twilight, when the radiant lies highest in a dark sky. With an entry velocity of 44 kilometers per second, a majority of these meteors will appear to move at moderate speeds.

The Eta Aquariids (ETA) are particles from Halley's Comet, produced in Earth-crossing orbits many centuries ago. We pass closest to these orbits from May 3 through the 7th. During this period the Eta Aquariids are at their best, capable of producing ZHR's of sixty. The actual visible rates are most often less than half this figure due to the low altitude of the radiant at dawn. Observed hourly rates at maximum normally vary from zero at 60 degrees north latitude to 25 near the equator and back down to near zero again in Antarctica, where the radiant elevation is very low. Hourly rates are now anywhere from zero to twenty per hour depending on your latitude and observing conditions. The radiant is currently located at 22:24 (336) -01. This area of the sky is located in northern Aquarius, close to the fourth magnitude star Gamma Aquarii. The best time to view this activity is just before the start of morning twilight, when the radiant lies highest in a dark sky. No matter your location these meteors will appear from the eastern sky and shoot in all directions. If the radiant has sufficient altitude Eta Aquariid meteors can also be seen shooting down toward the eastern horizon. With an entry velocity of 66 kilometers per second, a majority of these meteors will appear to move swiftly with a high percentage of the bright meteors leaving persistent trains.

As seen from the mid-northern hemisphere (45N) the Sporadic rates are low, but fairly steady. One would expect to see approximately seven random meteors during the last hour before dawn from rural observing sites and only one per hour during the evening hours. As seen from the mid-southern hemisphere (45S) morning rates would be near fourteen per hour as seen from rural observing sites and two per hour during the evening hours.

The table below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.

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  
             
Antihelion (ANT) - 15:44 (236) -20 30 02:00 1 – 2 II
Eta Lyrid (ELY) May 08 18:48 (282) +44 44 05:00 1 – <1 II
Eta Aquariid (ETA) May 05 22:24 (336) -01 66 08:00 10 – 10 II