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Meteor Activity Outlook for August 6-12, 2004

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  • Robert Lunsford
    This week will be another excellent time to view meteor activity. The moon reaches its last quarter phase on Saturday August 7. At this time the moon lies
    Message 1 of 1 , Aug 5, 2004
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      This week will be another excellent time to view meteor activity. The moon
      reaches its last quarter phase on Saturday August 7. At this time the moon
      lies ninety degrees west of the sun and will rise near 0100 local daylight
      time. While conditions this weekend will be less than perfect, the last
      quarter moon is significantly dimmer than the full moon and good meteor
      activity can still be observed. The estimated total hourly rates for
      evening observers this week should be near two for those in the Northern
      Hemisphere and two for those observers south of the equator. For morning
      observers the estimated total hourly rates should be near twenty five for
      those located in the Northern Hemisphere and twelve for those in the
      Southern Hemisphere. Rates are reduced during the morning hours due to
      moonlight. 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 radiant positions listed below are exact for Saturday night/Sunday
      morning August 7/8. These positions do not change greatly day to day so the
      listed coordinates 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 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 positions below are listed in a west to
      east manner in order of right ascension (celestial longitude). The positions
      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.
      These are the showers that may be observed this week:

      The Kappa Cygnids (KCG) are active from a wide radiant located at 18:56
      (284) +58. This position is located in southern Draco, four degrees
      northeast of the fourth magnitude star Kappa Cygni. Current rates would be
      near one shower member per hour. A large percentage of these meteors are
      bright, often fireball class meteors with brilliant colors. With an entry
      velocity of 25 km/sec. most of these meteors will appear to travel slower
      than average. The radiant is best placed near 2300 Local Daylight Time (11pm
      LDT) when it lies nearly overhead for much of the Northern Hemisphere. Due
      to its high northern declination this activity is not well seen from the
      Southern Hemisphere.

      The Alpha Capricornids (CAP) are active from a diffuse radiant located at
      21:04 (316) -06. This position lies in western Aquarius, five degrees west
      of the third magnitude star Sadalsuud (Beta Aquarii). The radiant is best
      placed near midnight local daylight time, when it lies highest in the sky.
      Current rates would be 1-2 shower members per hour at best. With an entry
      velocity of 23 km/sec., most activity from this radiant would be slow. This
      radiant is well seen except for far northern latitudes where it remains
      twilight all night long and the radiant does not rise as high into their
      sky.

      The Anthelion radiant is now centered at 22:00 (330) -11. This area of the
      sky is located on the Capricornus/Aquarius border, four degrees southwest of
      the fourth magnitude star Theta Aquarii Since this radiant is large and
      diffuse, any slow to medium speed meteor from eastern Capricornus,
      southwestern Pegasus, northern Piscis Austrinus or southwestern Aquarius
      could be a candidate for this shower. The center of this area 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 one shower member per hour north of the
      equator and two per hour for those situated south of the equator. At this
      time of year the Anthelion radiant overlaps both the Alpha Capricornid and
      North Delta Aquarid radiants so distinguishing between these showers will be
      difficult but not impossible if you face toward this general area of the
      sky.

      Unlike most of the annual showers the antihelion source is produced by
      debris from unknown objects orbiting in a direct motion like the earth.
      These objects are most likely asteroids, which produce stony and metallic
      debris whose density is much greater than material produced by comets. There
      is also the possibility that some of this activity may be caused by the
      "Jupiter family of comets", comets which have been altered by Jupiter's
      gravity into much shorter orbits. This material 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 source is active
      all year from an area of the sky nearly opposite that of the sun. The center
      of this source will move approximately one degree eastward per day and
      travels through many different constellations over the course of a year. It
      may make sense to list these meteors as anthelions or "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. At this time of year the IMO has no designation
      for the anthelion radiant as it overlaps several other radiants as it moves
      through Capricornus and Aquarius during July and August.

      The South Iota Aquarids (SIA) are active from a radiant currently located at
      22:28 (337) -14. This area of the sky is located in central Aquarius, three
      degrees west of the fourth magnitude star Tau Aquarii. This position is also
      very close to the anthelion radiant and without plotting and velocity
      estimates, it would be impossible to separate meteors from the two sources.
      Maximum activity occurred on August 4 with an expected ZHR of two. Current
      rates would be near one shower member per hour. At 34 km/sec. the SIA's have
      virtually the same velocity as the anthelion meteors. This radiant is most
      active near 0100 LDT when it lies highest in the southern sky.

      The North Delta Aquarids (NDA) are currently active from a radiant located
      at 22:16 (334) -05. This area of the sky is located in northern Aquarius,
      three degrees southwest of the fourth magnitude star Gamma Aquarii. This
      position is also close to the anthelion radiant and care must be taken to
      distinguish meteors from these sources. At 42 km/sec. the NDA's are a bit
      faster than the antihelion meteors. This radiant is most active between 0200
      and 0300 LDT when it lies highest in the sky. Like many of the radiants
      active this time of year the NDA's are better seen from areas south of the
      northern tropics or 30 degrees north latitude. With maximum activity
      expected on August 8, current hourly rates, seen from the southern tropics,
      would be near four per hour.

      The South Delta Aquarids (SDA) are nearing the end of their activity for
      2004. The current radiant position lies at 23:12 (348) -13. This area of the
      sky is located in central Aquarius, four degrees northeast of the third
      magnitude star Delta Aquarii. The radiant is best positioned near 0300 local
      daylight time, when it lies highest in the sky. Expected hourly rates would
      be near one per hour at best. These meteors encounter the earth at a speed
      of 41 km/sec. which is a bit faster than average. Activity is best seen from
      the Southern Hemisphere where the radiant passes high overhead.

      The Perseids (PER) reach maximum activity on the morning of August 12 with
      an expected ZHR near one hundred. Actual rates will most likely be less,
      depending on local circumstances. The current radiant position lies at 02:44
      (041) +58, which is located in southeastern Cassiopeia, three degrees
      northwest of the fourth magnitude star Eta Persei. By August 12 it will have
      shifted to 03:04 (046) +58, which places it three degrees northeast of Eta
      Persei, still in extreme southeastern Cassiopeia. The radiant is well placed
      for those in the Northern Hemisphere during the last few hours before dawn.
      Due to the high northern declination (celestial latitude) of the radiant,
      rates seen from the Southern Hemisphere are very low or non-existent.
      Current Perseid rates for those observers north of the equator should be
      near ten per hour. At 59km/sec., Perseid meteors are usually swift, often
      exhibiting persistent trains.

      The Northern Apex radiant is now centered at 03:00 (045) +31. This position
      lies in southwestern Peresus, ten degrees south of the bright variable star
      Algol (Beta Persei). This position lies less than thirty degrees south of
      the Perseid radiant so those observers who view away from the Perseid
      radiant (meaning the Perseid radiant is not visible in their field of view)
      have a real chance of including these meteors in their Perseid count.
      Luckily this will only amount to two or three extra Perseids per hour and
      will not make a great deal of difference on the night of maximum activity.
      This area of the sky is best placed for viewing during the last dark hour
      before dawn when it lies highest in the sky. Since this radiant is large and
      diffuse, any meteor from southern Perseus, eastern Andromeda, northwestern
      Taurus, northern Aries or Triangulum could be a candidate from this source.
      Rates would be now close to two per hour for observers north of the equator
      and less than one per hour for those observers south of the equator.

      Like the anthelion area, both apex areas are active all year long and travel
      approximately one degree eastward per day. Unlike the anthelion 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. This is not really a
      "shower" per se, but an artificial radiant created by the Earth's motion
      through space. Meteors from both branches are normally included in the
      sporadic count. I feel it is a worthy project to see if it is possible to
      distinguish these meteors from the normal sporadic background. On rare
      occasions there are meteors with a zero inclination that radiate precisely
      from the apex point on the ecliptic, exactly 90 degrees west of the sun. In
      simplistic terms, these meteors are seldom seen since the Earth "sweeps
      clean" much of the material that shares the same orbit as our planet. Much
      more material 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.

      The Southern Apex source lies exactly 30 degrees south of its northern
      counterpart at 03:00 (045) +01. This position lies in western Cetus, two
      degrees south of the third magnitude star Menkar (Alpha Ceti). Like the
      northern apex, these meteors are best seen toward dawn when the radiant lies
      highest above the horizon in a dark sky. Since this radiant is also large
      and diffuse, any meteor from western Cetus, southeastern Aries, northwestern
      Eridanus or southwestern Taurus could be a candidate from this source. Rates
      would now be one per hour regardless of your location.

      The Sporadic rates for the Northern Hemisphere are now increasing. One would
      expect to see perhaps six random meteors per hour during the last hours
      before dawn from rural observing sites. This estimate and the morning
      estimate for the Southern Hemisphere do not include the apex meteors listed
      above. During the evening hours perhaps two random meteors can be seen per
      hour from the Northern Hemisphere. Rates seen from the Southern Hemisphere
      are now lower than those seen in the north with perhaps five random meteors
      being seen during the late morning hours and two per hour during the
      evening. Morning rates are reduced due to moonlight.

      Clear Skies!
      Robert Lunsford
      IMO Secretary-General
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