During this period the moon waxes from half illuminated to nearly full by the end of the period. This weekend the waxing gibbous moon will set during the early morning hours for locations in the mid-northern latitudes. This will allow a few hours of observations under dark skies between moonset and the start of morning twilight. This window of opportunity to view under dark conditions shrinks with each passing night until late in the week when there is interfering moonlight all night long. The estimated total hourly meteor rates for evening observers this week is near 2 for observers located in the northern hemisphere and 3 for observers located south of the equator. For morning observers the estimated total hourly rates should be near 8 as seen from mid-northern latitudes (45N) and 15 as seen from tropical southern locations (25S). 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 during this period 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 14/15. 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 far 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.
These sources of meteoric activity are expected to be active this week.
The center of the large Anthelion (ANT) radiant is currently located at 16:28 (247) -22. This position lies in southwestern Ophiuchus, very close to the area occupied by the 4th magnitude star known as omega Ophiuchi. This position also lies 5 degrees north of the 1st magnitude star known as Antares (alpha Scorpii). Due to the large size of this radiant, Anthelion activity may also appear from the nearby constellations of Libra, western Sagittarius, and Ophiuchus as well as Scorpius. This radiant is best placed near 0200 local Summer Time (LST), when it lies on the meridian and is located highest in the sky. Hourly rates at this time should be near 2 as seen from mid-northern latitudes and 3 as seen from tropical southern latitudes. With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.
The May beta Capricornids (MBC) were discovered by members of the Croatian Meteor Network. These meteors are active from May 16-21, with maximum activity occurring on the 19th. The current position lies at 20:31 (308) -16. This area of the sky lies in western Capricornus, 2 degrees southwest of the 3rd magnitude star known as Dabih (beta Capricorni). These meteors are best seen near during the last dark hour of the night when the radiant lies highest in a dark sky. These meteors are better seen from the southern hemisphere where the radiant rises higher into the sky before the start of morning twilight. Hourly rates, even at maximum are expected to remain less than 1. With an entry velocity of 68 kilometers per second, a majority of these meteors will appear to move swiftly. Meteors traveling west out the radiant would be difficult to distinguish from the stronger eta Aquariids.
The eta Aquariids (ETA) are particles from Halley’s Comet, produced in Earth-crossing orbits many centuries ago. The radiant is currently located at 22:56 (344) +02. This area of the sky is located in western Pisces near the intersections of the constellations of Pisces, Aquarius, and Pegasus. This area of the sky also lies 5 degree northeast of the fourth magnitude star known as Hydria (eta 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. Hourly rates this weekend will most likely be near 1 per hour as seen from the northern hemisphere and near 3 as seen from south of the equator. 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 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 9 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. Evening rates are reduced due to moonlight.
The list below offers the information from above in tabular form. Rates and positions are exact for Saturday night/Sunday morning except where noted in the shower descriptions.
|DATE OF MAXIMUM ACTIVITY
|RA (RA in Deg.) DEC
|Local Summer Time
|16:28 (247) -22
|2 – 3
|May beta Capricornids (MBC)
|20:31 (308) -16
|<1 – <1
|eta Aquariids (ETA)
|22:56 (344) +02
|1 – 3