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(meteorobs) Meteor Activity Outlook for July 20-26, 2001
The moon is new on Friday July 20th and will be out of the way for
morning observers during this entire period. The evening sky will have a
waxing crescent moon which will not pose a problem until late in this
period. 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 12 for the Northern Hemisphere and 15 for
those located 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 for meteor activity. The positions listed below are exact for
Saturday night/Sunday morning July 21/22. The positions do not change
greatly day to day so these positions may be used during this entire
period.
The Alpha Capricornid radiant is located at 20:04 (301) -12. This area
of the sky is located at the intersection of the constellations of
Sagittarius, Aquila, and Capricornus just 3 degrees west of the naked
eye double star Alpha Capricorni. 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 producing
1-2 meteors per hour, depending on the elevation of the radiant above
your horizon. 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 20:24
(306) +47. This position is located in central Cygnus 3 degrees
northwest 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 20:56 (314) -16. This area of
the sky is located in north central Capricornus 2 degrees northwest of
the 4th magnitude star Theta Capricorni. Any slow to medium speed
meteor from Capricornus or western Aquarius may be a good candidate for
this shower. Due to the many radiants currently active in this region
this source would be extremely difficult to distinguish and will most
likely be inadvertently combined with the Capricornid or Aquarid totals
even by experienced meteor observers. 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 Aquarid radiant is currently located at 21:24 (321)
-09. This area of the sky is located in western Aquarius 4 degrees south
of the 3rd magnitude star Sadalsuud (Beta Aquarii). Like the Alpha
Caps this radiant lies within the boundaries of the antihelion radiant
area. The NDA's are noticeably faster 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. At this time expect to see only 1 shower member
per hour.
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 2-3 per hour but this will quickly rise as we
approach the date of maximum activity. The current radiant position lies
at 22:20 (335) -18. This area of the sky is located in a rather blank
area of southern Aquarius. Deep sky observers are familiar with this
position as it lies close to the large planetary nebula known as the
Helix Nebula. 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 can pass overhead.
The Pisces Austrinid radiant is currently located at 22:24 (336) -32.
This position lies in central Pisces Austrinus very close to the 4th
magnitude star Beta Piscis Austrini. These meteors are of average
velocity, slower than the Aquarids but faster than the Alpha Caps and
the antihelion meteors. Expect to see 0 to 1 an hour from the Northern
Hemisphere and 1-2 per hour south of the equator.
The Northern Apex radiant is now located at 01:56 (029) +26. This
position lies in southern Triangulum 4 degrees northwest of the 2nd
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 Triangulum, northeastern 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
would be less at 0-1 per hour. These meteors appear very much like the
Perseids and are often mistaken for early Perseids by those not facing
toward this portion of the sky. 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 01:56 (029) -04. This position lies in central Cetus 7
degrees south of the 4th magnitude star Al Rischa (Alpha Piscium). 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 now active in the morning sky producing 1-2 meteors per
hour as seen from the Northern Hemisphere. The radiant location is at
01:20 (020) +53 which places it on the Cassiopeia\Perseus border 3
degrees southeast of the 4th magnitude star Theta Cassiopeiae. 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 beginning to increase. One would expect to see perhaps
5 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. During the
evening hours perhaps 2 random meteors can be seen per hour from the
Northern Hemisphere. Rates seen from the Southern Hemisphere are at
their highest level of the year with perhaps 8 random meteors being seen
per hour during the late morning hours and 3 per hour during the
evening. Southern observers had better enjoy these strong rates now
since rates will soon plummet to far below those seen from the Northern
hemisphere.
Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
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