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(meteorobs) Meteor Activity Outlook for June 6-12, 2003
The moon reaches its first quarter phase on Saturday June 7. At this time
the moon will lie approximately ninety degrees east of the sun and will set
sometime near 0100 local daylight time. While the moon will interfere with
evening observations, late morning viewing will be unaffected until the
middle of next week. The estimated total hourly rates for evening observers
this week should be near one for northern viewers and two 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 twelve
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 evening sky
this week.
The radiant positions listed below are exact for Saturday night/Sunday
morning June 7/8. 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 Omega Scorpids are listed among the radiants of the Dutch Meteor
Society. I once felt these meteors were part of the antihelion complex but
they now seem to be a separate source. The peak is listed as June 4 with a
ZHR of 5. Actual observed rates would be less unless one lives deep in the
Southern Hemisphere. The current radiant position is 16:12 (243) -20. This
area of the sky is located in western Scorpius, two degrees east of the
third magnitude double star Acrab (Beta Scorpii). The best time to view this
activity is near midnight, local daylight time, when the radiant lies on the
meridian and is positioned highest in the sky. With an entry velocity of 21
kilometers per second, these meteors will appear to move slowly.
The Antihelion source is now centered at 18:04 (271) -23. This area of the
sky is located in western Sagittarius, only one degree north of M8, the
famous Lagoon Nebula. Since this source is large and diffuse, any slow to
medium speed meteor from northeastern Scorpius, western Sagittarius,
southwestern Serpens Cauda or southeastern Ophiuchus 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 Northern Apex area is now centered at 23:04 (346) +10. This position
lies in southern Pegasus, five degrees south of the third magnitude star
Markab (Alpha 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, western Pisces or northeastern
Aquarius could be a good candidate for this shower. This source should
provide at least 2 meteors per hour no matter your location.
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 23:04 (346) -20. This position lies in southern Aquarius, one
degree northwest of the fourth magnitude star 88 Aquarii. 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 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 located at 03:00 (045) +23. This area of the sky is located in
eastern Aries, twelve degrees east of the second magnitude star Hamal (Alpha
Arietis). This position is only thirty degrees southwest 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 one random meteor can be seen per hour.
Rates seen from the Southern Hemisphere would also be approximately six
random meteors being seen per hour during the late morning hours and two
during the evening hours.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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