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(meteorobs) Meteor Activity Outlook forJune 26-July 3, 2003
The moon reaches its new phase on Sunday June 29. At this time the moon will
lie in the vicinity of the sun as seen from the Earth. Therefore there will
not be any lunar interference at all this week. This is an important week
for meteor observers as the June Bootids may produce some rare activity. See
the shower profile below. 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 twelve for those located in the Northern
Hemisphere and sixteen 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.
The radiant positions listed below are exact for Saturday night/Sunday
morning June 28/29. 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 June Bootids reach maximum activity on June 27th near 1930 universal
time. This timing favors the Middle East, Southeastern Europe and southern
Asia. While an outburst would be surprising, seeing any activity at all
would be of high importance, even from areas not mentioned above. The
radiant is located at 14:56 (224) +47. This area of the sky is located in
northern Bootes some fifteen degrees southeast of Alkaid (Eta Ursae
Majoris), the last star in the handle of the "Big Dipper". Due to the
northern declination this shower is well seen only from the southern
equatorial areas northward to the northern temperate areas. Those located
north of 50 degrees north latitude will have difficulty seeing any activity
due to the very short nights experienced in those latitudes this time of
year. This area of the sky is best placed as soon as it gets dark during the
evening hours. At 18 km/sec. any June Bootids will appear to move quite
slowly compared to most meteors. Please make viewing this radiant a priority
this week!
The Theta Ophiuchids reach maximum activity on the 28th with very low rates.
The radiant is currently located at 16:40 (250) -11. This area of the sky is
located in southern Ophiuchus, only 1 degree east of the third magnitude
star Zeta Ophiuchi. 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 19:28 (292) -21. This area of the
sky is located in eastern Sagittarius, four degrees east of the fourth
magnitude star Pi Sagittarii. Since this source is large and diffuse, any
slow to medium speed meteor from Sagittarius or western Capricornus 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 up to four shower members per hour from locations
south of the equator and two 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 22:48 (342) -12, which places it in western
Aquarius, some five degrees northeast 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 00:28 (007) +18. This position
lies in central Pisces, four degrees northeast 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 eastern Pegasus, southwestern Andromeda
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 00:28 (007) -12. This position lies in western Cetus, seven
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
western Cetus or southern Pisces 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 01:44 (026) -11, which places it in
eastern Cetus, two degrees southeast of the fourth magnitude star Zeta Ceti.
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 Sporadic rates for the Northern Hemisphere are now rising toward their
peak, which occurs during the last quarter of the year. One would expect to
see perhaps five 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 six random meteors
being seen per hour during the late morning hours and three during the
evening hours.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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