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(meteorobs) Meteor Activity Outlook for April 16-22, 2004

The moon reaches its new phase on Monday April 19. At this time the moon
lies near the sun as seen from the Earth's surface and will rise and set
with the sun. As the week progresses the moon will appear in the evening sky
as a thin waxing crescent but will not interfere with meteor observing. 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. 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 April 17/18. 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 Pi Puppids (PPU) is a relatively new shower with most of the activity
occurring when the parent comet (26P Grigg-Skjellerup) is near perihelion.
This comet was last at perihelion in October 2002 so a trace of activity
from this shower is not out of the question. The radiant for this shower
lies far to the south and is nearly impossible to detect north of thirty
degrees north latitude. The current radiant position lies at 07:12
(108) -45.  This area of the sky is located in southwestern Puppis, some ten
degrees northeast of the brilliant negative one magnitude star Canopus
(Alpha Carinae). The radiant lies highest in a dark sky as soon as it
becomes dark at the end of evening twilight. Peak activity is not expected
until April 23 so current rates would be much less than one per hour. With
an entry velocity of only 18 kilometers per second, these meteors will
appear to move very slowly. Shower members are usually quite bright which
may also aid in their identification.

The Antihelion radiant is now centered at 14:48 (222) -15. This area of the
sky is located in western Libra, two degrees west of the third magnitude
star Zubenelgenubi (Alpha Librae). Since this radiant is large and diffuse,
any slow to medium speed meteor from western Libra or eastern Virgo 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 Sagittarids (SAG).

The Northern Apex radiant is now centered at 19:48 (297) -05. This position
lies in southern Aquila, five degrees southwest of the third magnitude star
Theta Aquilae. 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 Aquarius, northwestern
Capricornus, southern Delphinus, or Aquila 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 19:48 (297) -35. This position lies in southeastern
Sagittarius, three degrees west of the fourth magnitude star Theta
Sagittarii. 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 western Microscopium or
southeastern Sagittarius 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 Lyrids (LYR) are the first major annual shower of the season. ZHR's
reach one on April 16th and remain at or above this level through April 25.
Peak rates will occur on Thursday morning April 22. The predicted time of
maximum is near 0400 Universal Time, which favors Western Europe and
northwestern Africa. Regardless of your location, the best rates will be
seen on Thursday morning April 22. ZHR's average 18 but raw visual rates can
vary from 5-25, depending on your observing conditions. The radiant
currently lies at 17:48 (267) +34. This area of the sky is located in
eastern Hercules, five degrees southeast of the third magnitude star Pi
Herculis. On the morning of maximum activity it will have shifted to 18:04
(271) +34. The radiant rises in the northeastern sky during the late evening
hours for most locations in the Northern Hemisphere. One should wait until
the radiant reaches an elevation of thirty degrees before commencing
observations. At lower elevations the horizon would block most of the
activity producing very low counts. For 30 degrees north latitude this
occurs near midnight. The radiant would reach thirty degrees elevation
earlier for locations further north and later for locations further south.
The best time to view this activity is just before the start of morning
twilight, when the radiant lies highest in a dark sky. With an entry
velocity of 49 kilometers per second, a majority of these meteors will
appear to move with moderate to swift speeds. The Lyrids are also known to
produce a fair amount of meteors with persistent trains and an occasional
fireball.

The Sporadic rates for the Northern Hemisphere are declining. 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 do not include the apex meteors listed
above. During the evening hours perhaps two random meteors can be seen per
hour from the Northern Hemisphere. Rates seen from the Southern Hemisphere
are now stronger than those seen in the northern skies with perhaps eight
random meteors being seen per hour during the early morning hours and three
per hour during the evening.

Clear Skies!
Robert Lunsford
AMS Operations Manager

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