During this period the moon reaches its first quarter phase on Tuesday May 6th. At this time the half-illuminated moon will lie 90 degrees east of the sun and will be present in the evening sky until it sets around 0100 local daylight time (LDT), as seen from mid-northern latitudes. This weekend conditions will be even better as the waxing crescent moon will be less bright and will set earlier in the evening, allowing observers more time to view under truly dark conditions. The estimated total hourly meteor rates for evening observers this week is near 2 for observers situated at mid-northern latitudes and 3 for observers viewing from the southern tropics (latitude 25 S.). For morning observers the estimated total hourly rates should be near 14 for observers situated at mid-northern latitudes and 21 for observers viewing from the southern tropics. 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 this week due to moonlight. Note that the hourly rates listed below are estimates as viewed from dark sky sites away from urban light sources. Observers viewing from urban areas will see less activity as only the brightest meteors will be visible from such locations.
The radiant (the area of the sky where meteors appear to shoot from) 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 sources of meteoric activity are expected to be active this week:
The center of the large Anthelion (ANT) radiant is currently located at 15:44 (236) -20. This position lies on the Libra-Scorpius border, 4 degrees northwest of the 2nd magnitude star known as Dschubba (Delta Scorpii). These meteors may be seen all night long but the radiant is best placed near 0200 LDT when it lies on the meridian and is positioned highest in the sky. Due to the large radiant area, meteors from this source may also appear to radiant from the constellation of Serpens Caput, northwestern Scorpius, eastern Hydra, northern Lupus, and southwestern Ophiuchus as well as Libra. Rates at this time should be near 1 per hour no matter your location. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.
The Eta Aquariids (ETA) are particles from Halleys Comet, produced in Earth-crossing orbits many centuries ago. We pass closest to these orbits from May 5 through the 9th. During this period the Eta Aquariids are at their best, capable of producing zenith hourly rates (ZHRs) of 60. 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 30 near the equator and back down to near zero again in Antarctica, where the radiant elevation is again very low. Hourly rates this weekend will most likely be 5-10 per hour as seen from mid-northern latitudes. The radiant is currently located at 22:28 (337) -02. This area of the sky is located in northern Aquarius, two degrees southeast of the fourth magnitude star known as Sadalachbia (Gamma Aquarii). The best time to view this activity is during the hour before the start of morning twilight, when the radiant lies highest in a dark sky. With the radiant low in the east it would be best to face halfway up in the sky in that same direction. If the radiant has sufficient altitude Eta Aquariid meteors can also be seen shooting down toward the eastern horizon. With an entry velocity of 68 kilometers per second, a majority of these meteors will appear to move swiftly with a high percentage of the bright meteors leaving persistent trains. Surprisingly, this shower produces very few fireballs.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately 5 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 1 per hour. As seen from the tropical southern latitudes (25S), morning rates would be near 8 per hour as seen from rural observing sites and 2 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.
The table below presents a list of radiants that are expected to be active this week. Rates and positions are exact for Saturday night/Sunday morning except where noted in the shower descriptions.
|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|
|Anthelions (ANT)||–||15:44 (236) -20||29||02:00||1 – 1||II|
|Eta Aquariids (ETA)||May 07||22:28 (337) -02||68||09:00||8 – 12||I|