Meteor Activity Outlook for April 27-May 6, 2007

May provides the peak of the Eta Aquarid meteor shower. This is the strongest shower visible from the southern hemisphere but unfortunately this year glare from the waning gibbous moon will obscure all but the brightest meteors. The much weaker Eta Lyrids peak on May 9 under slightly better conditions. Sporadic rates seen in the northern hemisphere are nearing the nadir of their activity curve. The lowest rates are observed in June. On a positive note, rates seen from the southern hemisphere are increasing toward a July maximum.

During this period the moon reaches its full phase on Wednesday May 2. At this time the intensely bright moon will rise near sunset and set near sunrise. This weekend there is a small window of opportunity to view meteor activity in dark skies during the time between moonset and the start of morning twilight. This window increases as one moves south due to the fact that nights are longer in southern locations this time of year. The estimated total hourly rates for evening observers this week is near one for those north of the equator and two for observers south of the equator. For morning observers the estimated total hourly rates should be near seven for those located in the northern hemisphere and twenty for those viewing from 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. Evening rates are reduced all this week due to the intense moonlight. Morning rates become more affected as we approach the night of the full moon.

The radiant positions listed below are exact for Saturday night/Sunday morning April 28/29. 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. Doing this 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 Antihelion (ANT) radiant is now centered at 15:24 (231) -19. This area of the sky is centered in eastern Libra, five degrees northwest of the second magnitude star Dschubba (Delta Scorpii). 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 one per hour as seen in the northern hemisphere and two per hour for those located south of the equator. With an entry velocity of 30 km/sec., the average antihelion meteor would be of medium-slow speed.

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 over 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 thirty shower members per hour as seen from the northern tropical areas southward. Current rates would vary from zero to ten per hour depending on your latitude and observing conditions. The radiant is located at 22:04 (331) -03. This area of the sky is located in northern Aquarius, three degrees south of the third magnitude star Sadalmelik (Alpha 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.

Sporadic rates are slowing decreasing for observers in the northern hemisphere and slightly rising for those south of the equator. One would expect to see perhaps seven random meteors during the last hour before dawn from rural observing sites located in the northern hemisphere. During the first dark hour after the end of evening twilight, perhaps one random meteor can be seen per hour. Sporadic rates increase as the night progresses so rates seen near midnight would be near three per hour. Late morning sporadic rates seen from the southern hemisphere are now near fourteen per hour from rural observing sites. During the first dark hour after the end of evening twilight, perhaps two random meteors can be seen per hour, increasing to seven by midnight. Evening rates are reduced all this week due to the intense moonlight. Morning rates become more affected as we approach the night of the full moon.