Meteor Activity Outlook for April 25-May 1, 2008

Meteor activity picks up a bit during April as two major showers are active during the month. The first of these, the Lyrids, are active from the 16th through the 25th, with a pronounced maximum on the 22nd. Unfortunately this date coincides with a full moon this year so activity will be reduced. The Eta Aquarids start appearing near the 20th and reach maximum activity during the first week in May. 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) rise this month toward a maximum in July.

During this period the moon reaches its last quarter phase on Monday April 28th. At this time the moon will be located ninety degrees west of the sun and will rise near 0100 local daylight time (DST). During this period the slow evening hours will be free of moonlight while the moon will shine brightly during the morning hours. Successful meteor observations can be undertaken if you observe with the moon at your back or toward the darkest portion of the sky. Dry, transparent skies will help immensely as far less moonlight will be scattered allowing fainter stars, thus fainter meteors to be seen. 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 six. For those located in the mid-southern hemisphere (45 S) morning rates would be near ten 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. Morning rates are reduced by moonlight.

The radiant positions and rates listed below are exact for Saturday night/Sunday morning April 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 Pi Puppids (PPU) is a relatively new shower with most of the activity occurring when the parent comet (26P Grigg-Skjellerup) is near perihelion. This comet was at perihelion this past March but no activity of this shower has been reported so far. The radiant for this shower lies far to the south and is nearly impossible to detect north of thirty degrees north latitude. The radiant position lies at 07:18 (110) -45. This area of the sky is located in southern Puppis, two degrees southwest of the third magnitude star Sigma Puppis. The radiant lies highest in a dark sky as soon as it becomes dark at the end of evening twilight. Peak activity occurred on April 23, but a few shower members may be detected up to April 28. With an entry velocity of only 18 kilometers per second, these meteors will appear to move very slowly. Shower members are usually quite bright which may also aid in their identification.

The large Antihelion (ANT) radiant is now centered at 15:16 (229) -18. This area of the sky lies in central Libra, two degrees north of the faint star Iota Librae. Actually any meteor from western Scorpius, eastern Hydra, 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 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. Early in the activity period, as we are now, hourly rates would vary from zero to two per hour depending on your latitude and observing conditions. The radiant is currently located at 22:00 (330) -04. This area of the sky is located in northern Aquarius, four 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. 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 four 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 seven per hour as seen from rural observing sites and two per hour during the evening hours. Morning rates are reduced due to moonlight.

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  
             
Pi Puppids (PPU) Apr 23 07:18 (110) -45 18 18:00 0 – <1 II
Antihelion (ANT) - 15:16 (229) -18 30 02:00 1 – 2 II
Eta Aquariid (ETA) May 05 22:00 (330) -04 66 08:00 1 – 1 II