(meteorobs) Meteor Activity Outlook for May 31-June 6, 2002

Meteor Activity Outlook for 
May 31-June 6, 2002

By Robert Lunsford 
AMS Visual Program Coordinator

The moon reaches its last quarter phase on Monday June 3rd. At this time it rises near 01:00 local daylight time and will interfere somewhat with morning observing. The estimated total hourly rates for evening observers this week should be near 1 for those in the Northern Hemisphere and 2 for those south of the equator . For morning observers the estimated total hourly rates should be near 6 for those located in the Northern Hemisphere and 10 for those in the Southern Hemisphere. 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.  Morning rates are reduced slightly due to lunar interference.

The positions listed below are e xact for Saturday night/Sunday morning June 2/3. The positions do not change greatly day to day so these positions may be used during this entire period. Most star atlas's (available at science stores and libraries) 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 location. Meteor activity is not seen from radiants that are located below the horizon. The radiants below are listed in a west to east manner in order of right ascension (celestial longitude). The radiants listed first are located further west therefore are accessible earlier in the night while those listed last rise later in the night. This list also provides the order of ascending velocity for each radiant with those listed first usually being much slower than those last on the list. Velocity should not be the prime factor for shower association as all showers can produce slow meteors. Slow meteors can be produced from normally swift showers, such as the Leonids, when meteors appear near the radiant or close to the horizon. The true velocity is only revealed in shower members seen far from the radiant and high in the sky.

The Omega Scorpids appear on the list of DMS radiants. This display is predicted to peak on Sunday June 2 with a ZHR of 5. The moon and southerly declination will make observing any of these meteors difficult. The radiant position lies at 15:56 (239) -20 which would place it on the Libra-Scorpius border just west of the 3rd magnitude double star Acrab (Beta Scorpii). It would be best to watch for this activity near midnight local daylight time when the radiant lies on the meridian and is positioned highest in the sky. With an entry velocity of only 21 km/sec. any activity from this radiant would be extremely slow.  

The Antihelion radiant is now located at 17:48 (267) -23. This area of the sky is located in northwestern Sagittarius 8 degrees northeast of the 3rd magnitude star Theta Ophiuchi. The radiant lies low in the southeast at dusk and remains above the horizon the remainder of the night. This area of the sky is best placed near 0200 local daylight time when it lies on the meridian and is highest in the sky. At this time expect to see 1 meteor per hour from the Northern Hemisphere and perhaps 2 per hour south of the equator. Any slow to medium speed meteor from northwestern Sagittarius, southern Serpens Cauda or southwestern Ophiuchus could be a candidate for this shower.

Unlike most of the annual showers the antihelion radiant is produced by debris from unknown sources orbiting in a direct motion, like the earth. These sources are most likely asteroids, which produce stony and metallic debris, whose density is much greater than that produced by comets. This debris collides with the earth on the inbound portion of its orbit, before its closest approach to the sun. Therefore we best see them just after midnight when we are directly facing the path of these particles. The antihelion radiant is active all year from an area of the sky nearly opposite that of the sun. The radiant will travel approximately one degree eastward per day and travels through many different constellations over the course of a year. It is easiest to simply list these meteors as "ANT " but a majority of meteor organizations prefer that you list them from the constellation in which the radiant is currently located or the constellation where the shower reaches maximum activity. Those who share reports with the I.M.O. should label these meteors as Sagittarids (SAG).

The Northern Apex radiant is now located at 22:48 (342) +09. This position lies in southern Pegasus very close to the 4th magnitude star Sigma Pegasi. This area of the sky is best placed for viewing during the last dark hour before dawn. Since this radiant is diffuse any meteors from southern Pegasus or western Pisces could be a good candidate for this shower. This source should provide 1-2 meteors per hour during the last few hours before dawn regardless of your location. 

Like the antihelion radiant both apex radiants are active all year long and travel approximately one degree eastward per day. Unlike the antihelion debris these particles orbit the sun in a retrograde motion opposite that of the earth and are most likely produced by unknown comets. They strike the earth after their closest approach to the sun. Since they are moving in opposite directions these particles strike the earth at tremendous velocities often creating bright meteors with persistent trains. These particles strike the earth on the morning side of earth and are best seen just before morning twilight while the sky is still perfectly dark. There are meteors with a zero inclination that radiate precisely from the apex point on the ecliptic, exactly 90 degrees west of the sun. These meteors are rare though as the earth orbits the sun it has "swept clean" much of the material that shares the same orbit. Much more debris is located just north and south of the earth's orbit with slightly higher or lower inclinations. This creates the northern and southern branches of the apex activity. Meteors from both branches are normally included in the sporadic count but should also be noted in some manner as to which branch of the apex complex they appear to radiate.

The Southern Apex source lies exactly 30 degrees south of its northern counterpart at  22:48 (342) -21 . This position lies in central Aquarius, some 5 degrees southwest of the 3rd magnitude star Delta Aquarii. Any activity from this position could be a candidate from this source. Due to the southern declination (celestial latitude) rates would be now close to 2 per hour from the Southern Hemisphere and less 1 per hour from the Northern Hemisphere.

The Arietids are active from a radiant located just west of the sun. Being located there, 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   02:48 (042) +21 which is located in eastern Aries near the 4th magnitude star Epsilon Arietis. This shower peaks on June 6 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 have now bottomed out and will slowly begin to rise during June and July. One would expect to see perhaps 3 random meteors per hour during the last hours before dawn from rural observing sites. During the evening hours perhaps 1 random meteor can be seen per hour. These estimates and the morning estimates for the Southern Hemisphere do not include the apex meteors listed above. Rates seen from the Southern Hemisphere would be approximately 4 random meteors being seen per hour during the late morning hours and 2 during the evening hours. Morning rates for both hemispheres are reduced due to lunar interference.

Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator