[Prev][Next][Index][Thread]

(meteorobs) Meteor Activity Outlook for Aug. 10-16, 2001



The moon reaches its last quarter phase on Sunday August 12th.  The
evening sky will now be totally free of moonlight while the morning sky
endures a waning moon. The estimated total hourly rates for evening
observers this week should be near 5 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 40 (falling to
25 late in the period) for the Northern Hemisphere and 10 for those
located in the Southern Hemisphere. These rates are reduced due to
moonlight. 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 11/12. 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 moon free evening
period. The radiant position lies at 21:16 (284) +58 which actually
places it in Draco near the 5th magnitude star Omicron Draconis. This is
7 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. Maximum activity occurs on
August 17 this year.

The North Iota Aquarid radiant reaches a ZHR of 1 on August 11. Unless
you live in the Southern Hemisphere don't expect to see much activity
from this source until near its August 19 maximum. The current radiant
position lies at 21:16 (319) -07. This position is extremely close to
the Alpha Capricornid radiant which is soon ending. Like the Alpha 
Caps the NIA's are slow no matter where one sees them in the sky. They
are best seen near 0100 local daylight time (0000 local standard time)
when it lies highest in the sky. 

The Alpha Capricornid radiant is located at 21:20 (320) -05. This area
of the sky is located in western Aquarius 3 degrees northwest of the 3rd
magnitude star Sadalsuud (Beta Aquarii). 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. The Alpha Caps 
are near the end of their activity period so low rates of less than 1
per hour are to be expected. 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. 

The Antihelion radiant is now located at 22:16 (334) -10. This area of
the sky is located in central Aquarius 3 degrees southeast of the 4th
magnitude star Theta Aquarii. Any slow to medium speed meteor from
Aquarius or northeastern Capricornus 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 Aquarids reached maximum activity on August 8. The
radiant is currently located at 22:28 (337) -05. This area of the sky is
located in central Aquarius 5 degrees south of the 4th magnitude star
Eta Aquarii. Like the Alpha Caps and the North Iota Aquarids 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 1-2 shower members
per hour from the Northern Hemisphere and 2-3 per hour south of the
equator.

The South Iota Aquarid radiant is located at 22:44 (341) -14 which lies
very close to the 4th magnitude star Tau 2 Aquarii located in
southeastern Aquarius. This is still another radiant close to the
antihelion radiant. At 34 km/sec. They are just a bit faster than the
antihelion meteors. This radiant is also best placed between 0200 and
0300 LDT or 0100 to 0200 local standard time when it is located highest
in the southern sky. This showers peaked on August 4 this year so
current rates would be near 1 per hour at best.

The South Delta Aquarids are now well past maximum activity but still
should provide a couple of meteors per hour to the morning activity,
especially for observers in the Southern Hemisphere. The current radiant
position lies at 23:20 (350) -13. This area of the sky is located in
southeastern Aquarius 3 degrees south of the 4th magnitude star Psi 3 
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. These meteors encounter the earth at 41 km/sec., which is a
bit faster than average.

The Northern Apex radiant is now located at 03:16 (049) +33. This
position lies in southern Perseus some 10 degrees northwest of the
famous Pleiades star cluster. 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,  northern Aries, or 
northeastern 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 03:16 (049) +03.  This position lies on the Taurus/Cetus
border close to the faint star Kappa 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 eastern Cetus, southeastern
Aries,  or southwestern Taurus could be a candidate from this source.
Rates should be close to 2 per hour from most locations.

The Perseids will reach maximum activity on Sunday morning August 12.
The radiant location is at 03:04 (046) +58 which places it on the
Perseus/Cassiopeia border 5 degrees north of 3rd magnitude Gamma 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. Unfortunately a last 
quarter moon 50 percent illuminated will share the sky not far away in
Aries. Therefore there will be two strategies to use this year when
trying to see Perseid activity. One plan would be to watch during the
evening hours on Saturday August 11 when the moon is below the horizon.
One may be able to see up to 10 Perseids per hour depending on your 
latitude and sky conditions. Watching at this time is not practical
south of the equator as the radiant will not clear the horizon until
after midnight. Watching at this time will offer low rates but the
chance at seeing spectacular Perseid earthgrazing meteors. With the
Perseid radiant lying close to the northern horizon any Perseid meteor
encountering the earth will just graze the earth's upper atmosphere at a
more or less parallel angle. This allows each particle to last several
seconds and create a long path across the sky. This phenomena is best
seen near 30 degrees north latitude at dusk and then proceeds southward
as the night progresses. Unfortunately with the radiant near the horizon
only 1 or 2 of these meteors clear the horizon each hour. As stated
above higher northern latitudes may be able to see up to 10 Perseids per
hour during the evening hours but these will not be earthgrazers as the
Perseid radiant will be higher in their sky allowing the Perseid meteors
to enter the atmosphere at a steeper angle creating shorter paths in the
sky.

The second strategy would be to watch during the last few hours before
dawn with the radiant lies high in the northeastern sky. With the bright
moon in Aries one may expect to see up to 40 Perseids per hour. In 1982,
similar circumstances allowed me to count up to 38 Perseids per hour as
seen from dry transparent mountain skies. Observers watching from urban
areas or under hazy skies will seen much less activity. If viewing at
this time it would be wise to face away from the moon toward the north
or northwest. Those south of the equator will probably do better to look
toward the south if the moon lies in your northern sky. Look high enough
so that all you see is sky. It does no good to waste the bottom of your
field of view on the ground! There is no need to look straight up as
this direction is closer to the moon. When facing north Perseid meteors
will come from your upper right but can appear in any part of your field
of view. Those appearing close to the radiant will be short and move
slowly since they are coming toward you.  Those seen near the horizon
will also be slower and shorter as they are moving away from you. Those
seen far from the radiant and high in the sky will appear much longer
and faster. Perseid meteors are noted for their brilliant colors and
many persistent trains. They don't often reach maximum activity on a
weekend so despite the moonlight take advantage of this circumstance.
Perseid meteors are not visible south of approximately 35 degrees south
latitude.

The Sporadic rates for the Northern Hemisphere are now near 4 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 3 random meteors can be seen per hour from the Northern
Hemisphere. Rates seen from the Southern Hemisphere are now declining
rapidly with perhaps 3 random meteors being seen per hour during the
late morning hours and 1 per hour during the evening. Moonlight
interferes with morning viewing as seen from both hemispheres. 

Clear Skies!
Robert Lunsford
AMS Visual Program Coordinator
To stop getting email from the 'meteorobs' list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html