(meteorobs) Meteor Activity Outlook for May 10-16, 2002

Meteor Activity Outlook for 
May 10-16, 2002

By Robert Lunsford 
AMS Visual Program Coordinator

The moon is new on Saturday May 12 . At this time it will lie close to the sun and will be totally out of the way for nighttime viewing. This will be the best week of the month for meteor 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 10 for those located in the Northern Hemisphere and 13 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.   

The positions listed below are e xact for Saturday night/Sunday morning May 11/12. 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 16:24 (246) -21. This area of the sky is located in western Scorpius 5 degrees north of the brilliant orange star Antares (Alpha Scorpii). 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 eastern Libra, northwestern Scorpius 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 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 Sagittarius (SAG).

The Beta Corona Australids are listed among the radiants of the Dutch Meteor Society. They reach maximum on May 16 with a ZHR of only 3. Since the radiant reaches the zenith for only far southern latitudes most of us will see one or less per hour. This shower cannot be seen north of latitude 50N. The current radiant position lies at 18:36 (279) -41, which places it in central Corona Australis. The radiant lies highest in the sky at 0430 local daylight time. At 45 km/sec. an average shower member would possess medium velocity.

The Eta Lyrids are remnants of comet Iras-Araki-Alcock, which approached the earth back in 1983. The orbit of the comet lies close enough to the earth between May 4 and May 18 to produce minor activity. This fact was not widely realized in the world that existed before the WWW and email. Dutch and Japanese observers did observe modest activity from this radiant in the years following the comet's passage. Their results have shown that these meteors are exceeded only by the Eta Aquarids and Lyrids during the spring months in the Northern Hemisphere. They reach maximum activity on May 10 with an estimated ZHR of 7. Observed rates would most likely be far less than 7 per hour. The current radiant position lies at 19:20 (290) +44, which places it on the Lyra/Cygnus border, 4 degrees southwest of the 3rd magnitude star Delta Cygni. The radiant lies highest in the sky after sunrise so activity is best seen during the last few dark hours before morning twilight. At 44 km/sec. an average shower member would possess medium velocity. Thanks to DMS member Carl Johannink for his insight on this shower.

The Northern Apex radiant is now located at 21:24 (321) +01. This position lies in northwestern Aquarius 7 degrees north of the 3rd magnitude star Sadalsuud (Beta Aquarii). 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 southwestern Pegasus, Equuleus or northwestern Aquarius 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.  Don't mix these up with Eta Aquarid meteors which appear quite similar from a nearby radiant.

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  21:24 (321) -29 . This position lies on the border of Microscopium and Pisces Austrinus . 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 eastern Microscopium, western Pisces Austrinus or southern Capricornus 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 Eta Aquarids reached maximum activity on Sunday morning May 5. Hourly rates at maximum were much less than expected this year. This week would normally provide 1-5 ETA's per hour but 1-2 per hour is now more likely. The radiant is currently located at   22:52 (343) +01 which places it in extreme western Pisces, close to the border with Aquarius. This area of the sky does not rise until near 3am local daylight time for most locations so the activity window ranges from less than an hour in high northern latitudes to several hours south of the equator. The average Eta Aquarid meteor is swift and often leaves a persistent train. 

The Sporadic rates for the Northern Hemisphere are now in decline and will do so until June. One would expect to see perhaps 5 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. Rates seen from the Southern Hemisphere would be approximately 6 random meteors being seen per hour during the late morning hours and 2 during the evening hours.   

Clear Skies!
Robert Lunsford