With the arrival of May, observers in the tropical areas of the world are enjoying good views of the Eta Aquarids during the morning hours. The Antihelion radiant moves from eastern Libra, through northern Scorpius and into southern Ophiuchus during May. These areas of the sky are south of the celestial equator, favoring observers watching from south of the equator. Northern observers still suffer with low sporadic rates, especially during the evening hours. This situation will not improve until mid-July, when sporadic rates dramatically rise for northern observers. The overall meteor activity is much like April, possibly slightly better in the south and slightly worse in the north. The most favorable time to view meteor activity this month would be during the first week of the month, when the Eta Aquarids are near maximum activity.
During this period the moon will reach its first quarter phase on May 5. At this time the moon will set near 0100, allowing the early morning hours to be free of interfering moonlight. As the week progresses the waxing gibbous moon will remain in the morning sky later and later. Near the end of this period the nearly full moon will seriously hamper any attempt for successful observing. The estimated total hourly rates for evening observers this week is near one for observers in the northern hemisphere and two for those south of the equator. For morning observers the estimated total hourly rates should be near twenty for those in the northern hemisphere and thirty for those south of the equator. 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. Rates are reduced during the evening hours due to lunar interference.
The radiant positions listed below are exact for Saturday night/Sunday morning May 6/7. 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. 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 Antihelion (ANT) radiant is now centered at 15:56 (239) -20. This area of the sky is located on the Libra- Scorpius border, ten degrees northwest of the orange first magnitude star Antares (Alpha Scorpii). This radiant is best placed near 0200 local daylight time when it lies on the meridian and is highest in the sky. Rates at this time should be near two per hour for those north of the equator and three per hour 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 (IAA) are produced by comet IRAS-Araki-Alcock, which passed very close to the Earth twenty three years ago this May. Weak activity from this radiant has been seen in most years from May 5 through May 17, with maximum activity occurring on May 9. The current radiant position is located at 19:04 (286) +44. This area of the sky is located in northeastern 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 Aquarids (ETA) are particles from Halley’s Comet, which last passed through the inner solar system in 1986. Even though this is now twenty years ago, material is still encountered every year in late April and throughout most of May. We pass closest to Halley’s orbit on May 6. At that time Eta Aquarid rates can reach 30 shower members per hour as seen from the northern tropical areas southward. The radiant is located at 22:36 (339) -01. This area of the sky is located in central Aquarius, very close to the position occupied by the fourth magnitude star Eta 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. With an entry velocity of 66 kilometers per second, a majority of these meteors will appear to move swiftly.
The Sporadic rates for the Northern Hemisphere are now nearing their annual minimum activity. One would expect to see perhaps six random meteors per hour during the last hours before dawn from rural observing sites. During the evening hours perhaps one random meteor can be seen per hour. Sporadic rates seen from the southern hemisphere are now increasing toward a secondary maximum in July. One would see approximately eight random meteors per hour during the late morning hours and two per hour during the evening. Evening rates are reduced due to moonlight.