During June observers in the northern hemisphere see some of their lowest rates of the year. During this month the sporadic rates bottom out producing an average of only one meteor every ten minutes, even from dark sky sites. The active showers are also modest this month, barely adding any more activity to the nighttime scene. Observers south of the equator are enjoying some of their best rates of the year. This activity is produced from strong sporadic rates and the fact that the Antihelion radiant is positioned well south of the celestial equator this time of year. Combine this activity with long nights and the core of the Milky Way riding high in the sky, and you get an impressive scene. Unfortunately we have so few southern observers to enjoy this scenario. This is a reason that observations from south of the equator are so important. The short nights in the northern hemisphere often make June the least active month for meteor observers. Those who live in the more temperate latitudes should make every effort to view the elusive June activity and to report their valuable data.
This week the moon will reach its first quarter phase on Saturday June 3rd. At this time the moon will set near 0100 local daylight saving time, allowing the more active morning hours to be free of interfering moonlight. As the week progresses the waxing gibbous moon will remain in the sky most of the night, limiting the window that one may view under optimum conditions. The estimated total hourly rates for evening observers this week is near two for observers in the northern hemisphere and three for those south of the equator. For morning observers the estimated total hourly rates should be near eight for those in the northern hemisphere and eighteen for those south of the equator. 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. Evening rates are reduced due to moonlight.
The radiant positions listed below are exact for Saturday night/Sunday morning June 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. 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 Tau Herculids (THE) are produced by comet 73P/Schwassmann-Wachmann , which is currently making headlines as it passed close to the Earth. This shower was once included in many shower lists. As our understanding of the shower dynamics increased with this shower it became apparent that this shower is visible only on rare occasions when the Earth passes through the trails of debris produce by this comet. Therefore the Tau Herculids have been removed from most lists and are only rarely discussed. With the close approach of 73P/Schwassmann-Wachmann to the Earth in 2006, there exists the small possibility that some activity may be seen from this shower during the first week of June. The Earth already passed the node of the comet on May 31 so no strong activity is expected. A few stragglers are not out of the question though. Using the IMO’s shower parameters listed at: http://www.imo.net/files/data/vmdb/vmdbrad.txt, I have calculated that the radiant for this shower will be located near 15:12 (228) +40 this weekend. This area of the sky is located in northeastern Bootes, three degrees west of the third magnitude star Beta Bootis. The actual radiant of shower members may differ significantly due to the fragmentation of this comet and the very slow entry velocity. The best time to view possible activity is near midnight when the radiant lies highest in the sky. This shower is well placed for viewing in the northern hemisphere as it passes through the zenith for those located at 40N latitude. At extreme northern latitudes the length of the night is shortened appreciably, limiting the time one can view activity. As one progresses southward the length of night increases but the radiant altitude decreases. South of the equator the radiant altitude becomes a major factor, reducing the possibility of seeing any activity from this source. The radiant does not rise above the horizon south of 50S latitude. With an entry velocity of only 15 kilometers per second, these meteors will appear to move slowly, helping to aid in their identification. A great majority of these meteors will possess an angular velocity less than 5 degrees per second with the highest possible angular velocity certainly being less than 10 degrees per second. Please report any positive sightings to the AMS, the IMO News list, or Meteorobs as soon as possible after your observation.
The Antihelion (ANT) radiant is now centered at 17:44 (266) -23. This area of the sky is located on the Ophiuchus/Sagittarius border, five degrees northeast of the third magnitude star Theta Ophiuchi. This radiant is best placed near 0200 local daylight time when it lies on the meridian and is highest in the sky. Rates at this time should be near two per hour for those north of the equator and three per hour south of the equator. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.
The Daytime Arietids (DAR) are active from a radiant located approximately thirty degrees west of the sun. The radiant rises just before the start of morning twilight and any activity would be seen shooting upwards from the northeastern horizon. These meteors are of medium velocity and usually last several seconds as they skim the outer regions of the earth’s atmosphere. The current radiant position is located at 02:52 (043) +21, which is located in central Aries ten degrees southeast of the second magnitude star Hamal (Alpha Arietis). This shower peaks on June 7 with a ZHR of 60. Even with such strong rates the unfavorable altitude at the time of daybreak makes seeing this activity a difficult challenge. On the other hand, those with radio meteor equipment can easily detect this activity as it is the strongest annual radio meteor shower of the year.
The Sporadic rates for the Northern Hemisphere are now at their annual minimum activity. One would expect to see perhaps six random meteors per hour during the last hours before dawn from rural observing sites. During the evening hours perhaps two random meteors can be seen per hour. Sporadic rates seen from the southern hemisphere are now increasing toward a secondary maximum in July. One would see approximately fifteen random meteors per hour during the late morning hours and three per hour during the evening. These morning rates may appear a bit inflated but keen observers under pristine skies can easily verify an average of one random meteor every four minutes. Of course those viewing from less than optimal conditions will witness much less activity.