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(meteorobs) Meteor Activity Outlook for February 21-27, 2003
The moon reaches its last quarter phase on Sunday February 23. At this
time the moon will rise near midnight and will be a nuisance to anyone
viewing during the prime early morning hours. Towards the end of the
period the moon will be approaching new and will not be nearly the
problem it presented early in the week. The estimated total hourly rates
for evening observers this week should be near 2 for everyone regardless
of location. For morning observers the estimated total hourly rates
should be near 9 for those located in the Northern Hemisphere and 14 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 rates seen during the
morning hours this week.
The positions listed below are exact for Saturday night/Sunday morning
February 22/23 The positions do not change greatly day to day so these
positions 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 radiants
below are listed in a west to east manner in order of right ascension
(celestial longitude). The radiants 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 following radiants will be
active this week:
The Delta Leonids peak on February 25 from a radiant located at 11:12
(168) +16. This area of the sky is located in eastern Leo very close to
the third magnitude star Theta Leonis. This position is close to the
antihelion source so care must be taken to separate the two. It is quite
possible that this radiant is a northern branch of the antihelion
source. The hourly rate, even at maximum, rarely exceeds one shower
member per hour. The best time to view this activity is near 0100 local
time, when the radiant lies on the meridian and at its highest point in
the sky. With an entry velocity of 23 kilometers per second, these
meteors will appear to move slowly.
The Antihelion source is now centered at 11:12 (168) +05. This area of
the sky is located in southeastern Leo, two degrees southwest of the
fourth magnitude star Sigma Leonis. Since this source is large and
diffuse, any slow to medium speed meteor from eastern Leo or western
Virgo could be a candidate for this shower. The area of the sky 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 2 shower members per
hour from all locations.
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 Virginids or "VIR".
The Theta Centaurids is the first of several radiants that are active in
Centaurus during late January and throughout the month of February. The
date of maximum activity was February 14 with a predicted ZHR of 4.
Current ZHR's would be near 1. The radiant lies at 14:40 (220) -45. This
position is in southwestern Lupus two degrees southwest of the second
magnitude star Alpha Lupi. Due to the southern declination this shower
is not well seen north of the northern tropical regions. It is possible
to see activity from the latitude of San Diego, CA as I have witnessed
several of these meteors during my February observations. This area of
the sky is best placed near 0500 local standard time when it lies
highest in the sky. At 60 km/sec. the Theta Centaurids produce meteors
of swift velocity.
The Northern Apex source is now centered at 16:12 (243) -06. This
position lies in western Ophiuchus just south of a pair of third
magnitude stars known as "Yeds" (Epsilon and Delta Ophiuchi). 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
northeastern Libra, southern Serpens Caput, southwestern Hercules or
northwestern Scorpius 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 source 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. 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 could 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 116:12 (243) -36. This position lies in western Scorpius,
ten degrees southwest of the orange first magnitude star Antares (Alpha
Scorpii). 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 northern Lupus, western Scorpius or southeastern Libra could
a candidate from this source. Rates should be near 3 per hour from the
Southern Hemisphere and less than 1 per hour from the Northern Hemisphere.
The Sporadic rates for the Northern Hemisphere are now slowly declining
and will do so until June. One would currently expect to see perhaps 5
random 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 2 random meteors can be seen per hour from the
Northern Hemisphere. Rates seen from the Southern Hemisphere are now
slightly stronger than those seen in the northern skies with perhaps 6
random meteors being seen per hour during the early morning hours and 2
per hour during the evening. Sporadic rates are reduced during the
morning hours due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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