(meteorobs) Meteor Activity Outlook for July 9-15, 2004

[Robert Lunsford]

The moon reaches its last quarter phase on Friday July 9. At this time the
moon lies ninety degrees west of the sun and rises near 0100 local daylight
savings time. This weekend the waning crescent moon will rise during the
early morning hours and obscure the faintest meteors. If one keeps the
bright moonlight out of your field of view you can hold successful meteor
watches. The estimated total hourly rates for evening observers this week
should be near two for those in the Northern Hemisphere and three for those
observers south of the equator. For morning observers the estimated total
hourly rates should be near ten for those located in the Northern Hemisphere
and twelve for those in the Southern Hemisphere. Morning rates are reduced
due to moonlight. 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 radiant positions listed below are exact for Saturday night/Sunday
morning July 10/11. The radiant positions do not change greatly day to day
so the listed coordinates may be used during this entire period. Most star
atlases (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 positions below are listed in a west to
east manner in order of right ascension (celestial longitude). The positions
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 activity from the Theta Ophiuchids (THE) is winding down and will soon
cease. A few shower members may still be seen from a radiant located at
17:48 (267) -09. This area of the sky is located in southwestern Ophiuchus
very close to the 3rd magnitude star Nu Ophiuchi. This area of the sky is
best placed near 2300 LDT (11pm local daylight time) when the radiant lies
on the meridian and highest in the sky. At 27 km/sec. the Theta Ophiuchids
are slow compared to most other showers.

The Alpha Capricornids (CAP) are active from a wide radiant located at 19:20
(290) -15. This position lies in northeastern Sagittarius, three degrees
north of the fourth magnitude star Rho Sagittarii. The radiant is best
placed near midnight local daylight time, when it lies highest in the sky.
Current rates would be low, only 1-2 shower members per hour at best. With
an entry velocity of 23 km/sec., most activity from this radiant would be
slow.  This radiant is well seen except for far northern latitudes where it
remains twilight all night long and the radiant does not rise as high into
their sky.

The Alpha Cygnids (ACG) are listed as the Psi Cygnids in the list of
radiants published by 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
Dr. Peter Jenniskens between 1980 and 1991. Their studies indicate a ZHR
near 3 at maximum activity on July 18. The radiant position is currently
located at 20:04 (301) +46. This position is located in central Cygnus, four
degrees west of the third magnitude star Delta Cygni. With an entry velocity
of 37 km/sec. these meteors are of average velocity. The radiant is best
placed near 0200 LDT 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 Anthelion radiant is now centered at 20:12 (303) -19. This area of the
sky is located in western Capricornus, seven degrees southwest of the third
magnitude star Dibih (Beta Capricornii). Since this radiant is large and
diffuse, any slow to medium speed meteor from western Capricornus, eastern
Sagittarius, southeastern Aquila or southwestern Aquarius could be a
candidate for this shower. The center of this area is best placed near 0100
local standard time when it lies on the meridian and is highest in the sky.
At this time expect to see one shower member per hour north of the equator
and three per hour for those situated south of the equator.  At this time of
year the Anthelion radiant overlaps the Alpha Capricornid radiant so
distinguishing between the two showers will be difficult but not impossible
if you include both radiants within your field of view.

Unlike most of the annual showers the antihelion source is produced by
debris from unknown objects orbiting in a direct motion like the earth.
These objects are most likely asteroids, which produce stony and metallic
debris whose density is much greater than material produced by comets. This
material 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 source is active all year from an area of the sky nearly
opposite that of the sun. The center of this source will move approximately
one degree eastward per day and travels through many different
constellations over the course of a year. It may make sense to list these
meteors as anthelions or "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 send their data to the International Meteor Organization should
call these meteors Sagittarids (SAG).

The South Delta Aquarids (SDA) radiant provides the strongest activity in
July. This radiant peaks in strength on July 27 with an average ZHR of 20.
Currently rates are only 1-2 per hour but this will quickly rise as we
approach late July. The current radiant position lies at 21:40 (325) -19.
This area of the sky is located in eastern Capricornus, two degrees south of
the fourth magnitude star Gamma Capricorni. The radiant lies low in the
southeast at dusk and is not well seen until it approaches the meridian near
0300 LDT. These meteors encounter the earth at a speed of 41 km/sec. which
is a bit faster than average. Activity is best seen from the Southern
Hemisphere where the radiant passes high overhead. At this early date in
July, observers in high northern latitudes will be lucky to see any activity
at all.

The Pisces Austrinids (PAU) are also just now coming to life with a current
ZHR of 1. Don't expect to see 1 an hour unless you live near 30 degrees
south latitude where the radiant passes high overhead between the hours of
0200 and 0300 LDT. The current radiant position lies at 21:44 (326) -35
which places it in southwestern Pisces Austrinus, two degrees southwest of
the 4th magnitude star Iota Piscis Austrini. These meteors are of average
velocity, slower than the Aquarids but faster than the Alpha Caps and the
anthelion meteors.

The Pegasids (JPE) are now active in the morning sky. They reach maximum
activity on July 9th with an estimated ZHR of 3. The radiant is located at
22:44 (341) +15, which places it in western Pegasus, four degrees west of
the second magnitude star Mirfak (Alpha Pegasi). These meteors are best seen
during the last dark hour before the start of morning twilight, when the
radiant lies highest above the horizon in a completely dark sky. At
70km/sec. the majority of Pegasid meteors will appear to travel swiftly.
This shower remains above a ZHR of 1 only until July 13 so don't waste a
clear morning if you wish to see any of this activity in 2004.

The Northern Apex radiant is now centered at 01:12 (018) +22. This position
lies in northeastern Pisces, three degrees southeast of the fourth magnitude
star Eta Andromedae. This area of the sky is best placed for viewing during
the last dark hour before dawn when it lies highest in the sky. Since this
radiant is large and diffuse, any meteor from northern Pisces, eastern
Pegasus, western Aries or Triangulum could be a candidate from this source.
Rates would be now close to two per hour for observers north of the equator
and one for those south of the equator.

Like the antihelion area, both apex areas 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. This is
not really a "shower" per se, but an artificial radiant created by the
Earth's motion through space. Meteors from both branches are normally
included in the sporadic count. I feel it is a worthy project to see if it
is possible to distinguish these meteors from the normal sporadic
background. On rare occasions there are meteors with a zero inclination that
radiate precisely from the apex point on the ecliptic, exactly 90 degrees
west of the sun. In simplistic terms, these meteors are seldom seen since
the Earth "sweeps clean" much of the material that shares the same orbit as
our planet. Much more material 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.

The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 01:12 (018) -08. This position lies in northern Cetus, two
degrees northeast of the third magnitude star Eta Ceti. Like the northern
apex, these meteors are best seen toward dawn when the radiant lies highest
above the horizon in a dark sky. Since this radiant is also large and
diffuse, any meteor from Cetus or southern Pisces could be a candidate from
this source. Rates would now be one per hour regardless of your location.

The July Phoenicids (PHE) peak on July 13 from a radiant located at 02:08
(032) -48. This area of the sky is located in western Phoenix some 3 degrees
west of the 4th magnitude star Chi Eridani. This area of the sky is best
placed for viewing during the last dark hour before dawn. Due to the extreme
southern declination (celestial latitude) this shower is not well seen north
of the Northern Tropics. The further south one is located the better
opportunity that shower members may be seen.  At 47 km/sec. these meteors
would be a bit faster than your average meteor. Rates are extremely variable
for this shower. Some years produce no activity at all while others see
notable activity. Data is urgently needed for this shower so southern
observers are strongly encourage to watch for any activity from this source.

The Sporadic rates for the Northern Hemisphere are now increasing. 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 do 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 still
slightly better than those seen in the north with perhaps 5 random meteors
being seen during the late morning hours and 3 per hour during the evening.
Morning rates are reduced due to moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager