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(meteorobs) Upcoming Meteor Activity

Meteor Activity Outlook for 
February 22-28, 2002

By Robert Lunsford 
AMS Visual Program Coordinator

The moon is full on Wednesday February 27. Early in this period one can watch between moon set and dawn under good conditions. After the weekend this window of opportunity becomes too small as the moon will set late in the morning. The estimated total hourly rates for evening observers this week should be near 1-2 regardless of location. This is less than normal due to moonlight. For morning observers the estimated total hourly rates should be near 13 for those located in the Northern Hemisphere and 17 for those located 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.
 
The positions listed below are exact for Saturday night/Sunday morning February 23/24. 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.
 
Activity from the Delta Leonids reach maximum activity on February 24 from a radiant is located at 11:12 (168) +16. This position is located in eastern Leo only 2 degrees east of the 3rd magnitude star Theta Leonis. This position is close to the antihelion radiant so care must be taken to distinguish meteors between the two radiants. With an entry velocity of 23 kilometers per second these meteors are slower than most meteors from the antihelion radiant.
 
The Antihelion radiant is now located at 11:16 (169) +04. This area of the sky is located in southeastern Leo 2 degrees south of the 4th magnitude star Sigma Leonis. Any slow to medium speed meteor from Leo or 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 least 2 shower members per hour from locations in the Northern Hemisphere. Observers south of the equator will most likely be limited to 1 per hour or less, owing to the lower radiant altitude. 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 Theta Centaurids continue to be active through the first two weeks of March. The radiant is located at 14:44 (221) -45 which lies in western Lupus 2 degrees north of 2nd magnitude Alpha Lupi. This part of the sky is best seen near 0500 local time when it reaches it highest altitude above the horizon. The maximum activity occurred on February 14 with ZHR's near 4. Current rates would be less than 2 per hour and perhaps less than 1 per night as seen from the Northern Hemisphere. With an entry velocity of 60 kilometers per second these meteors would have a swift apparent velocity.

The Northern Apex radiant is now located at 16:16 (244) -06. This position lies in western Ophiuchus only 2 degrees east of the 3rd magnitude star Yed Posterior (Epsilon 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 northeastern Libra,  western Ophiuchus, northwestern Scorpius or southern Serpens Caput could be a good candidate for this shower. This source should provide 2-3 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 16:16 (244) -36. This position lies in west-central Scorpius 8 degrees south of the brilliant orange star Antares (Alpha 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 northern Lupus or southwestern Scorpius could be a candidate from this source. Due to the extreme southern declination (celestial latitude) rates would be 3-4 per hour from the Southern Hemisphere and only 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 7-8 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 now be a bit better than those seen in the Northern Hemisphere with perhaps 8-10 random meteors being seen per hour during the late morning hours and 1-2 during the evening hours. rates would be reduced during the evening hours due to moonlight.

Clear Skies!
Robert Lunsford