During this period the moon reaches its new phase on Sunday the 20th. At this time the moon will be located near the sun and will not be visible at night. As the week progresses the waxing crescent moon will enter the evening sky but will not cause any problems with meteor observing. This is especially true for the morning hours when the moon will be below the horizon. The estimated total hourly rates for evening observers this week is near three for observers in the northern hemisphere and four for those south of the equator. For morning observers the estimated total hourly rates should be near seven as seen from mid-northern latitudes and thirteen from mid-southern latitudes. 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 (the area of the sky where meteors appear to shoot from) positions and rates listed below are exact for Saturday night/Sunday morning May 19/20. 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 currently located at 16:48 (252) -22. This position lies in southwestern Ophiuchus, six degrees northeast of the bright first magnitude orange star Antares (Alpha Scorpii). Due to the large size of this radiant, Antihelion activity may also appear from Scorpius , Libra, northern Lupus, western Sagittarius, southwestern Serpens Cauda, as well as southern Ophiuchus . This radiant is best placed near 0200 LDT, when it lies on the meridian and is located highest in the sky. Rates at this time should be near two per hour as seen from the northern hemisphere and three as seen from south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of slow velocity.
The last of the Eta Aquariids (ETA) will be seen this weekend from a radiant located at 23:12 (348) +04. This area of the sky is located in western Pisces, two degrees northwest of the fourth magnitude star Gamma Piscium. 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. Hourly rates this weekend will most likely be less than one per hour, no matter your location. With an entry velocity of 67 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 five sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near two per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near ten per hour as seen from rural observing sites and three per hour during the evening hours. Locations between these two extremes would see activity between the listed figures.
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|
|Antihelions (ANT)||–||16:48 (252) -22||30||02:00||2 – 3||II|
|Eta Aquariids (ETA)||May 07||23:12 (348) +04||67||09:00||<1 – <1||I|