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(meteorobs) Meteor Activity Outlook for October 11-17, 2002



Meteor Activity Outlook for 
 October 11-17, 2002

By Robert Lunsford 
AMS Operations Manager

The moon will reach its first quarter phase on Sunday October 13. At this time it sets near 0100 local daylight time, leaving the active morning hours free of interfering moonlight. Please note that the majority of activity this week is concentrated in a relatively small area of the sky. All of this activity will have similar characteristics so the only real way to tell them apart to is face toward Orion, Gemini, and Auriga so that their paths can be traced back with some degree of accuracy. The estimated total hourly rates for evening observers this week should be near 4 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 20 for those located in the Northern Hemisphere and 10 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 activity one may see 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 October 12/13. The positions do not change greatly day to day so these positions may be used during this entire period. Most star atlases (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 which constellations are in 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. 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 02:20 (035) +13. This area of the sky is located in a remote area  of southern Aries, 10 degrees southeast of the 2nd magnitude star Hamal (Alpha Arietis). Any slow to medium speed meteor from southern Aries or northern Cetus could be a candidate for this shower. The radiant 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 2 shower members per hour regardless of your location.

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 material 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. IMO observers may wish to list these meteors as Taurids or "STA or NTA's".

The Orionids are beginning to appear in the morning sky at rates near 2 per hour. The radiant is located at  06:00 (090) +15, which places it in northeastern Orion, 7 degrees northeast of the variable 1st magnitude star Betelgeuse (Alpha Orionis).  The radiant is best placed near 5am local daylight time, when it lies highest in the sky. These meteors are seen equally well from both hemispheres. At 66km/sec., the average Orionid is swift. This shower peaks on October 22, which coincides with the full moon. The best period to see the Orionids this month will be between the 15 and the 20th, after the moon has set.

The Epsilon Geminids will be appearing this week from a radiant located at 06:28 (097) +27 . This position is located in western Gemini 4 degrees northwest of the 3rd magnitude star Epsilon Geminorum. This shower reaches maximum activity on October 18 with an estimated ZHR of 3. Current rates would be near 1 shower member per hour. The radiant is best placed just before the start of morning twilight, when it lies highest in the sky. At 71km/sec., the average Epsilon Geminid would be swift, much like the Leonids of November. 

The Delta Aurigids peaked on the morning of October 10. Current rates would be 1-2 per hour as seen from the Northern Hemisphere. The radiant is located at 06:32 (098) +50, which places it in northern Auriga near the faint variable star Psi 1 Aurigae. Due to the extreme northern declination, this shower is only visible from the southern tropics northward. The radiant is best placed just before the start of morning twilight, when it lies highest in the sky. At 64km/sec., the average Delta Aurigid is swift. 

The Northern Apex radiant is now located at 07:20 (110) +37. This position lies in a remote area of eastern Auriga near the faint star 65 Aurigae. This is also 5 degrees northwest of the 2nd magnitude star Castor (Alpha Geminorum). 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 eastern Auriga, western Lynx or northern Gemini could be a good candidate for this shower. This source should provide at least 3 meteors per hour for those in the Northern Hemisphere and less than 1 per hour for those in the Southern Hemisphere.

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  07:20 (110) +07. This position lies in central Canis Minor, close to the 5th magnitude star Eta Canis Minoris. 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 Canis Minor could a candidate from this source. Rates would be now close to 2 per hour regardless of your location.

The Sporadic rates for the Northern Hemisphere have now reached their plateau of top activity, which occurs during the entire last quarter of the year. One would currently expect to see perhaps 9 random meteors per hour during the last hours before dawn from rural observing sites. This estimate and the morning estimate for the Southern Hemisphere does not include the apex meteors listed above. During the evening hours perhaps 4 random meteors can be seen per hour from the Northern Hemisphere. Rates seen from the Southern Hemisphere are now at their annual low with perhaps 5 random meteors being seen per hour during the early morning hours and 2 per hour during the evening. 

Clear Skies!
Robert Lunsford