During this period the moon reaches its last quarter phase on Sunday May 26th. At this time the half-illuminated moon rises between 0200 and 0300 local summer time (LST) and remains in the sky the remainder of the night. As the week progresses the moon will become less of a factor as it wanes and rises later with each passing night. The estimated total hourly meteor rates for evening observers this week is near 3 for those viewing from the northern hemisphere and 4 for those located south of the equator. For morning observers the estimated total hourly rates should be near 5 as seen from mid-northern latitudes (45N) and 10 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. Morning rates are reduced by moonlight during this period. 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 25/26. 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.
These sources of meteoric activity are expected to be active this week.
The tau Herculids (TAH) are an irregular shower not active every year. They are best known for being associated with comet Schwassmann-Wachmann 3 and the strong display seen in 1930. Due to recent activity from the comet, this shower could produce more activity in the upcoming decade. The Earth should pass closest to the particles from Schwassmann-Wachmann 3 around June 3rd. The current position of the radiant would be near 14:56 (224) +39. This area of the sky is located in northern Bootes, 2 degrees southwest of the 3rd magnitude star known as Nekkar (beta Bootis). This is not that close to the star tau Herculis, for which this shower is named. Apparently the discoverers of this display placed the radiant further east toward Corona Borealis and Hercules. It’s also possible that past displays had different radiant locations. This area of the sky is best placed near midnight LST, when it lies high overhead for observers located in mid-northern latitudes. With an entry velocity of 15 km/sec., the average tau Herculid meteor would be of very slow velocity.
The center of the large Anthelion (ANT) radiant is currently located at 17:08 (257) -23. This position lies in southern Ophuichus, just west of the brilliant planet Jupiter. This position also lies 4 degrees northwest of the 3rd magnitude star known as theta Ophiuchi. Due to the large size of this radiant, anthelion activity may also appear from eastern Sagittarius, northwestern Scorpius, as well as southern Ophiuchus. This radiant is best placed near 0200 local LST, when it lies on the meridian and is located highest in the sky. Rates at this time should be near 2 per hour as seen from mid-northern latitudes (45 N) and 3 per hour as seen from the southern tropics (S 25) . With an entry velocity of 30 km/sec., the average Anthelion meteor would be of slow velocity.
The June mu Cassiopeiids (JMC) were discovered by Dr, Peter Brown and associates using data from the Canadian Meteor Orbit Radar (CMOR) installation. These meteors are active from May 18-June 15, with maximum activity occurring on June 8th. The radiant position currently lies at 00:12 (003) +51. This area of the sky lies in southeastern Cassiopeia, 7 degrees southwest of the 2nd magnitude star known as Shedar (alpha Cassiopeiae). 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 northern hemisphere where the radiant rises higher into the sky before the start of morning twilight. Hourly rates are expected to be less than 1. With an entry velocity of 42 kilometers per second, a majority of these meteors will appear to move with medium velocities. Since these meteors were discovered by radar, they may be on the faint side and difficult to see unless one observes under optimal conditions.
The Daytime Arietids (ARI) are active from May 22-June 24 with maximum activity occurring on the June 8th. These meteors are difficult to catch as the radiant only lies 30 degrees west of the sun. Therefore the only time these meteors are visible is during the last dark hour before dawn. The radiant is currently located at 02:14 (034) +22. This area of the sky is located in western Aries, 2 degrees southeast of the 2nd magnitude star known as Hamal (alpha Arietis). Current rates are expected to be less than 1 no matter your location. With an entry velocity of 41 km/sec., the average meteor from this source would be of medium velocity.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately 4 sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near 2 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 3 per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning 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.
|SHOWER||DATE OF MAXIMUM ACTIVITY||CELESTIAL POSITION||ENTRY VELOCITY||CULMINATION||HOURLY RATE||CLASS|
|RA (RA in Deg.) DEC||Km/Sec||Local Summer Time||North-South|
|tau Herculids (TAH)||Jun 03||14:56 (224) +39||15||00:00||<1 – <1||III|
|Anthelion (ANT)||–||17:08 (257) -23||30||02:00||2 – 3||II|
|June mu Cassiopeiids (JMC)||Jun 08||00:12 (003) +51||42||09:00||<1 – <1||IV|
|Daytime Arietids (ARI)||Jun 08||02:14 (034) +22||41||11:00||<1 – <1||IV|