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(meteorobs) Meteor Activity Outlook



Meteor Activity Outlook for 
March 8-14, 2002

By Robert Lunsford 
AMS Visual Program Coordinator

The moon reached its last quarter phase on Wednesday March 6. At this time the moon will rise near midnight and be near the meridian at sunrise. The slow evening hours will be totally free of moonlight while the waning moon will cause some interference in the morning sky.  Successful observing at this time can be still be accomplished by simply keeping the moon at your back. During these times I will face northward and reacquaint myself with the constellations currently visible in the northern sky. The estimated total hourly rates for evening observers this week should be near 2 for everyone regardless of location. For morning observers the estimated total hourly rates should be near 7 for those located in the Northern Hemisphere and 15 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 by moonlight during this period.

The positions listed below are exact for Saturday night/Sunday morning March 9/10. 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 Antihelion radiant is now located at 12:12 (183) -01. This area of the sky is located in western Virgo 2 degrees southwest of the 4th magnitude star Eta Virginis. Any slow to medium speed meteor from western Virgo could be a candidate for this shower. This area of the sky is best placed near 0100 local standard time when it lies on the meridian and is highest in the sky. At this time expect to see at  on average 2 shower members per hour from most locations. 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 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 facing the direction from which this activity appears. 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 Virginids (VIR).

The Gamma Normids reach maximum activity on the 13th. The radiant is currently located at 16:24 (246) -51 which places it in central Norma only 1 degree south of the wide naked eye double star Gamma Normae. This location is also 25 degrees due south of the brilliant orange star Antares (Alpha Scorpii). Due to the extreme southern declination this shower is well seen only from the northern tropics southward. Even from favored locations ZHR's rarely surpass 5. This area of the sky is best placed just before the start of morning twilight. The Gamma Normids are of medium-swift velocity.

The Northern Apex radiant is now located at 17:12 (258) -08. This position lies in southern Ophiuchus some 8 degrees north of the 2nd magnitude star Eta Ophiuchi. 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 Ophiuchus or southwestern Serpens Cauda 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 "sweeps 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  17:12 (258) -38. This position lies in southeastern Scorpius some 3 degrees southwest of the bright pair of stars known as "cat eyes" (Shaula and Lesath, aka Lambda and Upsilon Scorpii). Like the northern apex these meteors are best seen toward dawn when the radiant lies highest above the horizon in a dark sky. Any meteor from southeastern Scorpius could be a candidate from this source. Due to the extreme southern declination (celestial latitude) rates would be now close to 3 per hour from the Southern Hemisphere and less 1 per hour from the Northern Hemisphere.

The Sporadic rates for the Northern Hemisphere are now in decline and will do so until June. One would expect to see perhaps 4-5 random meteors per hour during the last hours before dawn from rural observing sites. During the evening hours perhaps 1-2 random meteors can be seen per hour. Rates seen from the Southern Hemisphere would be approximately 6-8 random meteors being seen per hour during the late morning hours and 2-3 during the evening hours. Moonlight interferes with morning rates.

Clear Skies!
Robert Lunsford