[Prev][Next][Index][Thread]

(meteorobs) Meteor Activity Outlook for July 5-11, 2002



Meteor Activity Outlook for 
 July 5-11, 2002

By Robert Lunsford 
AMS Visual Program Coordinator

The moon is new on Wednesday July 10. At this time the moon will be in the vicinity of the sun and will not cause any problems whatsoever.  Observers this weekend will see a waning crescent moon in the morning sky. The estimated total hourly rates for evening observers this week should be near 2 for those in the Northern Hemisphere and 3 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 12 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 July 6/7. 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 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 Theta Ophiuchids reached maximum activity on June 28th with very low rates. The radiant is currently located at 17:16 (259) -10. This area of the sky is located in western Serpens Cauda, 3 degrees north of the 4th magnitude star Nu Serpentis. Due to the southern declination this shower is well seen only from the northern tropics southward. Even from favored locations ZHR's rarely surpass 2. This area of the sky is best placed near 2300 (11pm local daylight time) when the radiant lies on the meridian and highest in the sky. At 27 km/sec. the Theta Ophiuchids are slow compared to most other showers.

The Alpha Capricornid activity is just now beginning from a radiant located at 19:08 (287) -17. The area of the sky is located in northeastern Sagittarius 5 degrees north of the 3rd magnitude star Pi Sagittarii. This position is close to the antihelion radiant and unless you plot the meteors you see, these meteors will be indistinguishable from one another. The velocity of the Alpha Caps is 25 km/sec., which is slightly slower than the antihelion radiant. The radiant is best placed near 0100 local daylight time when it lies on the meridian. The Alpha Caps are known for their brightly colored fireballs which increase in frequency as we approach the July 29 maximum for this shower. 

The Antihelion radiant is now located at 19:56 (299) -20. This area of the sky is located in a remote area  of eastern Sagittarius. Any slow to medium speed meteor from western Capricornus or eastern Sagittarius 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 1 shower member per hour from locations north of the equator and 2 an hour from areas south of the equator.

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. Those who share reports with the I.M.O. should label these meteors as Sagittarids (SAG).

The Pegasids reach maximum activity on July 9 with a ZHR of 3. The current radiant position lies at  22:32 (338) +15. This area of the sky lies in central Pegasus some 7 degrees west of the 2nd magnitude star Mirfak (Alpha Pegasi). This area of the sky is best placed for viewing during the last dark hour before dawn when it lies highest in the sky.   At 70km/sec. the majority of Tau Aquarids will appear quite swift.

The Tau Aquarids are listed among the radiants of the Dutch Meteor Society. They reached maximum activity on June 29th with an estimated ZHR of 3. The radiant is currently located at 23:20 (350) -09, which places it in eastern Aquarius close to the naked eye triple star Psi Aquarii. Once again southern observers are slightly favored for this shower as the radiant rises higher into their sky before the onset of morning twilight. These meteors are best seen just before the start of morning twilight. At 63km/sec. the majority of Tau Aquarids appear quite swift.

The Northern Apex radiant is now located at 00:32 (056) +21. This position lies in northern Pisces 3 degrees south of the 4th magnitude star Eta Andromeda . 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 northern Pisces or southwestern Andromeda could be a good candidate for this shower. This source should provide at least 2 meteors per hour for those in the Northern Hemisphere and 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  00:32 (056) -09 . This position lies in western Cetus 3 degrees northwest of the 3rd magnitude star Eta Ceti. 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 central or western Cetus could be a candidate from this source. Rates would be now close to 2 per hour from the Southern Hemisphere and 1 per hour from the Northern Hemisphere.

The Tau Cetids are also listed among the radiants of the Dutch Meteor Society. They reached maximum activity on the June 27th with an estimated ZHR of 4. The radiant is currently located at 02:12 (033) -08, which places it in eastern Cetus some 5 degrees southwest of the brightening variable star Mira (Omicron Ceti). Once again southern observers are slightly favored for this shower as the radiant rises higher into their sky before the onset of morning twilight. These meteors are best seen just before the start of morning twilight. At 66km/sec. the majority of Tau Cetids appear quite swift. Be careful when trying to distinguish between the Tau Cetids, Southern Apex and the Tau Aquarids. These 3 radiants are relatively close in the sky and produce similar appearing, swift meteors.

The Sporadic rates for the Northern Hemisphere are now increasing. One would expect to see perhaps 5 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 2 random meteors can be seen per hour from the Northern Hemisphere. Rates seen from the Southern Hemisphere are still slightly better than those seen in the north with perhaps 6 random meteors being seen during the late morning hours and 3 per hour during the evening.   

Clear Skies!
Robert Lunsford