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(meteorobs) Meteor Activity Outlook for Aug. 17-23, 2001
The moon is new on Saturday August 18th freeing the morning skies from
lunar interference. The evening sky will have some interference from
moonlight late in this period. The estimated total hourly rates for
evening observers this week should be near 3 for those in the Northern
Hemisphere and 2 for those in the Southern Hemisphere. For morning
observers the estimated total hourly rates should be near 23 for the
Northern Hemisphere and 10 for those located in the Southern Hemisphere.
These rates also 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 for meteor activity.
The positions listed below are exact for Saturday night/Sunday morning
August 18/19. The positions do not change greatly day to day so these
positions may be used during this entire period.
The Kappa Cygnids can provide some low activity to the evening skies and
on into morning. The radiant position lies at 21:24 (286) +59 which
actually places it in Draco 2 degrees east of the 5th magnitude star
Omicron Draconis. This is 6 degrees northwest of Kappa Cygni. The Kappa
Cygnids seem temperamental and are either non-existent or quite active.
The expected rates are 1-2 per hour during the evening hours decreasing
later on during the morning as the radiant sinks into the northwest.
Activity is possible all night long as seen from the Northern
Hemisphere. Very low activity is possible for observers between 30
degrees south and the equator during the evening hours. This shower is
invisible south of 30 degrees south latitude. The shower members are
very slow and often bright with vivid colors. There have been reports of
fragmenting Kappa Cygnids as they slowing fall through the sky. With
maximum activity occurring on August 17 this year rates over the weekend
could be near 2 per hour.
The North Iota Aquarid radiant reaches maximum activity on August 19.
Rates will vary from 3 per hour as seen from the Southern Hemisphere to
less than 1 per hour from the high Northern Hemisphere. The current
radiant position lies at 21:44 (326) -06. This position is 3 degrees
east of the 3rd magnitude star Sadalsuud (Beta Aquarii). They are best
seen near 0100 local daylight time (0000 local standard time) when it
lies highest in the sky. These meteors are slow regardless where they
appear in the sky.
The Antihelion radiant is now located at 22:44 (341) -07. This area of
the sky is located in central Aquarius near the 4th magnitude star
Lambda Aquarii. Any slow to medium speed meteor from central Aquarius or
extreme western Pisces may be a good candidate for this shower. This
position is also only 4 degrees from the center of the North Delta
Aquarid radiant making the two radiant virtually indistinguishable. It
would be best at this time to label all meteors from this area NDA's.
This area of the sky is best placed near 0200 local daylight time (0100
local standard time) when it lies on the meridian. At this time expect
to see perhaps 2 per hour from all locations. 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 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.
The North Delta Aquarids reached maximum activity on August 8. The
radiant is currently located at 22:44 (341) -03. This area of the sky is
located in central Aquarius 4 degrees north of Lambda Aquarii and very
close to the antihelion radiant. The radiant is best placed between
0200 and 0300 LDT or 0100 to 0200 local standard time when it is located
highest in the southern sky. At this time expect to see 1-2 shower
members per hour. These meteors are of average velocity.
The South Delta Aquarids are now nearing the end of their activity.
Rates are now less than 1 per hour and will soon stop completely. The
current radiant position lies at 23:40 (355) -11. This area of the sky
is located in eastern Aquarius 3 degrees north of the faint twin stars
Omega Aquarii. The radiant lies low in the southeast at dusk and is not
well seen until it approaches the meridian near 0300 local daylight time
or 0200 LST. Like the NDA's, these meteors are of average or medium
velocity.
The Pi Eridanids are just now starting to appear in the late morning
sky. This radiant, listed among the radiants of the DMS catalog, will
reach maximum activity on August 27 with a ZHR of 4. Current rates would
be near 1 per hour. The radiant position is located at 03:00 (045) -18,
which places it western Eridanus 5 degrees north of the 4th magnitude
star Tau 3 Eridani. This area of the sky is better placed for observers
in the north tropical zone and areas further south. It lies highest in
the sky just before the onset on dawn. Like the Perseids these meteors
are swift if seen high in the sky far from the radiant. I would also
expect some trains from the brighter shower members.
The Gamma Doradids are another shower listed among the DMS radiants. The
radiant position lies at 03:40 (055) -52, which places it central
Horologium, 5 degrees west of the 4th magnitude star Gamma Doradus.
Many of you may have not heard of these far southern constellations
which lie some 50 degrees southwest of the well known constellation of
Orion. Obviously this radiant is best seen from the Southern Hemisphere.
Some activity may be glimpsed from the northern tropical areas just
before dawn. The date of maximum activity is August 30 so current rates
would be quite low, perhaps 1 per hour. Shower members possess an
average velocity of 41 km/sec., similar to the Delta Aquarid radiants.
The Northern Apex radiant is now located at 03:44 (056) +34. This
position lies in southern Perseus some 2 degrees northwest of the 3rd
magnitude star Xi Persei. 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 southern Perseus, northeastern Aries, or
northwestern Taurus could be a good candidate. As seen from the Northern
Hemisphere this source should produce at least 3 meteors per hour during
the last few hours before dawn. Rates seen from the Southern Hemisphere
would be much less at 0-1 per hour. These meteors appear very much like
the Perseids and are often mistaken for Perseids by those not facing
toward this portion of the sky. This may also be the source for the many
Perseid sub radiants reported throughout the years.
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 03:44 (056) +04. This position lies in southwestern
Taurus 7 degrees southeast of the 4th magnitude star Xi Tauri. 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
Cetus, southeastern Aries, northwestern Eridanus, or southwestern Taurus
could be a candidate from this source. Rates should be close to 2 per
hour from most locations.
The Perseids reached maximum activity on August 12 with widely variable
rates as expected with the moonlit conditions. Rates this weekend
should still be near 5 an hour. The current radiant location is at 03:44
(056) +59 which places it southwestern Camelopardalis some 10 degrees
northeast of the 2nd magnitude Mirfak (Alpha Persei). This area of the
sky is highest just before dawn so this would be the best time to try to
see any Perseid activity. Shower members are swift unless seen at the
radiant or close to the horizon.
The Sporadic rates for the Northern Hemisphere are now near 7 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 now declining
rapidly with perhaps 4 random meteors being seen per hour during the
late morning hours and 1 per hour during the evening. Moonlight
interferes slightly with evening viewing as seen from both hemispheres.
Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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