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 |
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