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(meteorobs) Meteor Activity Outlook for July 13-19, 2001
The moon reaches its last quarter phase on Friday July 13th. This means
that the evening skies are free from moonlight while the morning skies
suffer some limited interference. This interference becomes less of
a factor as the moon approaches its new phase on July 20. The estimated
total hourly rates for evening observers this week should be near 2 for
those in Northern Hemisphere and 3 for Southern Hemisphere observers.
For morning observers the estimated total hourly rates should be near 10
for the Northern Hemisphere and 13 for those located in the Southern
Hemisphere with some lunar interference. These rates assume that you are
watching from rural areas away from all sources of light pollution
except for the moon. 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 July 14/15. The
positions do not change greatly day to day so these positions may be
used during this entire period.
The July Phoenicids last only a week centered on its July 12 maximum.
The radiant lies at 02:20 (035) -47. This area of the sky is located in
southern Eridanus 8 degrees southwest of the 3rd magnitude star Acamar
(Theta Eridani). The DMS lists this radiant 8 degrees northwest of this
position in extreme eastern Phoenix. At 47 km/sec. these meteors would
be a bit faster than your average meteor. Due to the extreme southern
declination these meteors are not well seen north of 30 degrees N
latitude. It would be interesting for far southern observers to see
exactly where this radiant lies as it rises much higher in their sky. It
is best placed highest in the sky just before the beginning of morning
twilight.
The Alpha Capricornid radiant is located at 19:36 (294) -14. This area
of the sky is located in a remote area of northeastern Sagittarius. This
area also lies in the outer radiant area of the antihelion radiant. Any
meteor traveling east or west out of this area would be difficult to
classify. At this time rates of the Alpha Caps and the antihelion
radiant would be similar. With an entry velocity of 25 km/sec. the Alpha
Caps are just a bit slower than the antihelion meteors. The Alpha Cap
radiant is best placed near 0100 local daylight time (0000 local
standard time) when it lies on the meridian. This radiant is noted for
its colorful fireballs which will occur more frequently as we approach
the July 30 maximum.
The Alpha Cygnids are listed as the Psi Cygnids among the radiants of
the Dutch Meteor Society. No matter what you call them they are often
overlooked by the many other better known radiants active at this time.
This radiant was well represented in the studies coordinated by Peter
Jenniskens between 1980 and 1991. Their studies indicate a ZHR near 3 at
maximum activity on July 18. The radiant position is 20:12 (303) +46.
This position is located in central Cygnus 5 degrees west of the bright
star Deneb (Alpha Cygni). With an entry velocity of 37 kilometers per
second these meteors are of average speed. The radiant is best placed
for observing near 0200 LDT or 0100 local standard time 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 Antihelion radiant is now located at 20:28 (307) -18. This area of
the sky is located in western Capricornus near the 5th magnitude star
Rho Capricorni. Any slow to medium speed meteor from western
Capricornus, northeastern Sagittarius, southeastern Aquila, or
southwestern Aquarius may be a good candidate for this shower. 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 1 per hour from locations in the Northern Hemisphere and 2
meteors per hour from the Southern Hemisphere. 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 reach a ZHR (zenith hourly rate) of 1 on July
15. The date of maximum activity is not until August 8 so this low rate
of activity will prevail throughout most of July. The radiant is
currently located at 21:04 (316) -10. This area of the sky is located
in southwestern Aquarius 2 degrees northwest of the 4th magnitude star
Nu Aquarii. Like the Alpha Caps this radiant lies within the boundaries
of the antihelion radiant area. The NDA's are noticeably swifter than
the antihelion meteors at 42 km/sec. verses 30 km/sec. This 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. 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.
The South Delta Aquarid radiant provides the strongest shower of July.
This radiant peaks in strength on July 27 with an average ZHR of 20. At
this time rates are only 1-2 per hour but this will quickly rise as we
approach late July. The current radiant position lies at 21:56 (329)
-19. This area of the sky is located on the Aquarius/Capricornus border
4 degrees southeast of the 3rd magnitude star Nashira (Delta
Capricorni). 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. These meteors encounter the earth at 41 km/sec. which is a
bit faster than average. These meteors are better seen from the Southern
Hemisphere where the radiant passes overhead. At this time observers in
high northern will be lucky to seen any activity at all from this
radiant.
The Pisces Austrinids are also just now coming to life with a ZHR of 1.
Don't expect to see 1 an hour unless you live near 30 degrees south
latitude when the radiant passes overhead between 0200 and 0300 LDT. The
current radiant location is 22:00 (330) -34 which places it in southern
Pisces Austrinus 1 degree southwest of the 4th magnitude star Mu Piscis
Austrini. These meteors are of average velocity, slower than the
Aquarids but faster than the Alpha Caps and the antihelion meteors.
The Northern Apex radiant is now located at 01:28 (022) +24. This
position lies in eastern Pisces 9 degrees west of the 2rd magnitude star
Hamal (Alpha Arietis). 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 western Aries could be a good candidate.
As seen from the Northern Hemisphere this source should produce at least
2 meteors per hour during the last few hours before dawn. Rates seen
from the Southern Hemisphere should be slightly less at 1 per hour. 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 01:28 (022) -06. This position lies in central Cetus 3
degrees northeast of the 4th magnitude star (Theta 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 Cetus or
southern Pisces could be a candidate from this source. Rates should
be close to 1 per hour from most locations.
The Perseids are just now coming to life with perhaps 1 Perseid meteor
visible every few hours in the morning sky. The radiant location is at
00:48 (012) +51 which places it in southern Cassiopeia approximately 10
degrees north of the Great Andromeda Galaxy. This area of the sky is
highest just before dawn so this would be the best time to try to see
any Perseid activity. These meteors are swift except when seen near the
radiant or near the horizon. They also produce many fine persistent
trains. The Perseids with become much more active as we approach their
August 12 maximum.
The Sporadic rates for the Northern Hemisphere have bottomed out and
will now finally begin to increase in July. One would expect to see
perhaps 4 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
but is reduced due to moonlight. 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 Northern with perhaps 5 random meteors being seen per hour
during the late morning hours and 3 per hour during the evening.
Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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