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(meteorobs) Meteor Activity Outlook for Feb 27-Mar 4, 2004
The moon reaches its first quarter phase on Saturday February 28. At this
time the moon lies ninety degrees east of the sun and will set near local
midnight. Observers this weekend will have excellent skies during the
morning hours after moonset. As the week progresses, the moon will set later
in the morning narrowing the window of opportunity to view under truly dark
conditions. The estimated total hourly rates for evening observers this week
should be near two for those in the Northern Hemisphere and three for those
south of the equator. For morning observers the estimated total hourly rates
should be near ten for those located in the Northern Hemisphere and fifteen
for those in the Southern Hemisphere. Evening 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 February 28/29. The radiants do not change greatly day to day so the
given 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 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 Delta Leonids (DLE) peaked on February 25 with a ZHR of two. Current
rates would be less than one per hour. The radiant is located at 11:28 (172)
+15. This area of the sky is located in eastern Leo, three degrees east of
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,
active this time of year. 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 radiant is now centered at 11:36 (174) +02. This area of the
sky is located on the Leo/Virgo, four degrees northwest of the fourth
magnitude star Beta Virginis. Since this radiant is large and diffuse, any
slow to medium speed meteor from southern Leo, western Virgo or northern
Crater 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 two shower members per hour
regardless of your location.
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 send their data to the International Meteor Organization
should call these meteors Virginids (VIR).
The Theta Centaurids (TCE) are near the end of their activity period for
2004. The date of maximum activity was February 15 with a predicted ZHR of
four. Current rates would be less than one per hour. The radiant lies at
15:00 (225) -47. This position lies in central Lupus, four degrees northeast
of the second magnitude star Alpha Lupi. This area of the sky is best placed
near 0500 local standard time when it lies highest in the sky. This shower
is not well seen north of the northern tropical regions. At 60 km/sec. the
Theta Centaurids produce meteors of swift velocity.
The Gamma Normids (GNO) are active from a radiant located at 15:40
(235) -52. This position lies in western Norma, five degrees west of the
third magnitude star Zeta Lupi. Since the date of maximum activity is not
until March 13, current ZHR's would still be less than 1. Due to the far
southern declination of the radiant, this shower is not well seen north of
the northern equatorial regions. This area of the sky is best placed near
0600 local standard time when it lies highest in the sky. At 56 km/sec. the
Gamma Normids normally produce meteors of swift angular velocities.
The Northern Apex radiant is now centered at 16:36 (249) -07. This position
lies in western Ophiuchus, four degrees north of the third magnitude star
Zeta Ophiuchi. 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 western Ophiuchus, eastern
Serpens Caput, northern Scorpius, southwestern Hercules or northern Libra
could be a candidate from this source. Rates would be now close to two per
hour regardless of 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 16:36 (249) -37. This position lies in the southern Scorpius,
three degrees southwest of the second magnitude star Epsilon Scorpii. 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 eastern Lupus, northern Norma or southern
Scorpius could be a candidate from this source. Rates would now be less than
one per hour in the Northern Hemisphere and three per hour in the Southern
Hemisphere.
The Sporadic rates for the Northern Hemisphere are now past their annual
peak. One would currently expect to see perhaps six 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 one random
meteor 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 eight random meteors being seen per hour during
the early morning hours and two per hour during the evening. Evening rates
are reduced due to moonlight.
Clear Skies!
Robert Lunsford
AMS Operations Manager
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