By Robert Lunsford
AMS Visual Program Coordinator
The moon is reaches its first quarter phase on Sunday May 19 . At this
time it sets near 01:00 local daylight time and will not interfere with
morning observing. The estimated total hourly rates for evening
observers this week should be near 1 for those in the Northern
Hemisphere and 1 for those south of the equator . For morning observers
the estimated total hourly rates should be near 8 for those located in
the Northern Hemisphere and 14 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.
Evening rates are reduced due to lunar interference.
The positions listed below are e xact for Saturday night/Sunday morning
May 18/19. 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 16:48 (252) -22. This area of
the sky is located in southwestern Ophiuchus 6 degrees northeast of the
brilliant orange star Antares (Alpha Scorpii). Many old time meteor
watchers will recall this radiant being called the Alpha Scorpiids this
time of year. 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 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 reached 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 19:12 (288)
-40, which places on the Corona Australis/Sagittarius border, just east
of Beta 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 Northern Apex radiant is now located at 21:48 (327) +03. This
position lies in southwestern Pegasus 5 degrees northwest of the 3rd
magnitude star Sadalmelik (Alpha 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
northern 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 21:48 (327) -27 . This position lies in a remote area of
western Pisces Austrinus, some 12 degrees northwest of the brilliant
white star Fomalhaut (Alpha Pisces Austrinus). Any activity from western
Pisces Austrinus, Microscopium 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 should provide 1-2 ETA's per hour just before dawn. The radiant is
currently located at 23:16 (349) +05 which places it in extreme western
Pisces near the faint star 7 Piscium. 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 1 during
the evening hours. Evening rates are reduced due to lunar interference.
Clear Skies!
Robert Lunsford
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