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(meteorobs) Meteor Activity Outlook for June 20-26, 2003



The moon reaches its last quarter phase on Saturday June 21. At this time
the moon will lie approximately ninety degrees west of the sun and will rise
sometime near 0100 local daylight time for those living in the midnorthern
latitudes. This weekend the moon will interfere with morning viewing, but
observers can compensate by keeping the moon out of their field of view. As
the week progresses the waning crescent moon will become less of a nuisance.
The estimated total hourly rates for evening observers this week should be
near two for northern viewers and three for those located south of the
equator. For morning observers the estimated total hourly rates should be
near six for those located in the Northern Hemisphere and eight for those 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 meteor activity.
Moonlight will reduce the activity seen in the morning sky this week.

The radiant positions listed below are exact for Saturday night/Sunday
morning June 21/22. The positions do not change greatly day to day so they
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 Theta Ophiuchids reach maximum activity on the 28th with very low rates.
The radiant is currently located at 16:08 (242) -12. This area of the sky is
located in northwestern Scorpius, only 1 degree east of the 4th magnitude
star Xi Scorpii. Due to the southern declination this shower is well seen
only from the northern temperate areas southward. Even from favored
locations ZHR's rarely surpass 2. This area of the sky is best placed near
2300 (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 Antihelion source is now centered at 19:00 (285) -23. This area of the
sky is located in central Sagittarius, only one degree southwest of the 4th
magnitude star Omicron Sagittarii.  Since this source is large and diffuse,
any slow to medium speed meteor from Sagittarius or southern Scutum could be
a candidate for this shower. This area of the sky is best placed near 0200
local daylight time when it lies on the meridian and is highest in the sky.
At this time expect to see two shower members per hour from locations south
of the equator and one per hour from locations further north.

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 antihelions 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 share their reports with the I.M.O. should call these
meteors Sagittarids or "SAG".

The Tau Aquarids are listed among the radiants of the Dutch Meteor Society.
They reach maximum activity on the 29th with an estimated ZHR of 3. The
radiant is currently located at 22:20 (335) -15, which places it in western
Aquarius, sharing the same position with the bright planet Mars. Once again
southern observers are favored for this shower as the radiant rises higher
into their sky before the onset of morning twilight. These meteors are best
seen just before the start of morning twilight. At 63km/sec. the majority of
Tau Aquarids appear quite swift.

The Northern Apex area is now centered at 00:00 (000) +15. This position
lies in southeastern Pegasus, three degrees west of the third magnitude
variable star Algenib (Gamma Pegasi). This area of the sky is best placed
for viewing during the last dark hour before dawn. Since this source is
large and diffuse any meteors from southern Pegasus, or western Pisces could
be a good candidate for this shower. This source should provide at least 2
meteors per hour from the Northern Hemisphere and one per hour from the
Southern Hemisphere.

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 00:00 (000) -15. This position lies in western Cetus, ten
degrees northwest of the second magnitude star Deneb Kaitos (Beta 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
northeast Pisces Austrinus, northwest Sculptor or southern Aquarius could a
candidate from this source. Rates should be near 2 per hour from the
Southern Hemisphere and 1 per hour from the Northern Hemisphere.

The Tau Cetids are also listed among the radiants of the Dutch Meteor
Society. They reach maximum activity on the 27th with an estimated ZHR of 4.
The radiant is currently located at 01:20 (020) -14, which places it in
central Cetus, four degrees southeast of the 3rd magnitude star Eta Ceti.
Once again southern observers are favored for this shower as the radiant
rises higher into their sky before the onset of morning twilight. These
meteors are best seen just before the start of morning twilight. At
66km/sec. the majority of Tau Cetids appear quite swift. Be careful when
trying to distinguish between the Tau Cetids, Southern Apex and the Tau
Aquarids. These 3 radiants are relatively close in the sky and produce
similar appearing, swift meteors.

The Arietids are active from late May throughout most of June. At peak
activity on June 8, they are one of the strongest meteor showers of the
year. Unfortunately the radiant is situated too close to the sun to allow
more than a meteor or two to be seen from this source each morning. The
radiant is currently located at 03:24 (051) +29. This area of the sky is
located in northeastern Aries, seven degrees northwest of the bright open
cluster known as the Pleiades (M45). This position is only forty degrees
west of the sun. The best time to view this activity is just before the
start of morning twilight, when the radiant lies just above the northeastern
horizon. Unfortunately observers in far northern latitudes will observe
morning twilight long before the radiant has a chance to rise. The situation
improves as one moves south with the most favorable areas lying within the
northern tropical latitudes. With an entry velocity of 38 kilometers per
second, a majority of these meteors will appear to move with moderate
speeds. A majority of the activity seen from this source are the so called
"earthgrazers", meteors that are very long and last for several seconds.

The Sporadic rates for the Northern Hemisphere have now reached their nadir.
One would expect to see perhaps four random meteors per hour during the last
hours before dawn from rural observing sites. This estimate and the estimate
for the Southern Hemisphere does not include meteors from the apex radiants.
During the evening hours perhaps two random meteors can be seen per hour.
Rates seen from the Southern Hemisphere would also be approximately five
random meteors being seen per hour during the late morning hours and three
during the evening hours. Rates are reduced in the morning hours due to
moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager

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