(meteorobs) Meteor Activity Outlook for April 15-21, 2005

Robert Lunsford lunro.imo.usa at cox.net
Thu Apr 14 13:52:48 EDT 2005


This upcoming period will see the moon reaching its first quarter phase on
Saturday April 16.  At this time the moon sets near 0100 local daylight
time, allowing the more active morning hours to be free of interfering
moonlight. As the week progresses, the moon will set later and later as it
waxes toward its full phase. Thus the window of opportunity for viewing
under ideal circumstances decreases as the week progresses. The estimated
total hourly rates for evening observers this week should be near one for
those in the Northern Hemisphere and two for those observers south of the
equator. Evening rates are reduced due to moonlight. For morning observers
the estimated total hourly rates should be near eight for those located in
the Northern Hemisphere and ten 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 16/17. These positions do not change greatly day to day so the
listed coordinates may be used during this entire period. Most star atlases
(available at science stores and planetariums) 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 latitude. 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 further down the list rise later in the night.

These are the showers that may be observed this week:

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 07:08
(107) -44. 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 Anthelion radiant is now centered at 14:44 (221) -15. This area of the
sky is located in western Libra, three degrees west of the third magnitude
star Zubenelgenubi (Alpha 2 Librae). Since this radiant is large and
diffuse, any slow to medium speed meteor from eastern Virgo, eastern Hydra
or Libra could be a candidate for this shower. The center of this area 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 no matter 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. There
is also the possibility that some of this activity may be caused by the
"Jupiter family of comets", comets which have been altered by Jupiter's
gravity into much shorter orbits. 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 anthelions 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. Observers who send their reports to the
International Meteor Organization (I.M.O.) should label these meteors as
Sagittarids (SAG).

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 Friday morning April 22. Unfortunately on that date
a nearly full moon will spoil most of the show. The predicted time of
maximum is near 1030 Universal Time, which favors the America's. Regardless
of your location, the best rates will be seen on Friday morning. ZHR's
average 18 but raw visual rates can vary from 5-25, depending on your
observing conditions. The radiant currently lies at 17:40 (265) +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 now reaching their low
plateau for the year. From now through June morning sporadic rates will
remain near five per hour. During the dark evening hours perhaps one random
meteor can be seen per hour. Sporadic rates seen from the Southern
Hemisphere are slowly increasing toward a July maximum. From south of the
equator one would expect to see approximately seven random meteors per hour
during the late morning hours and two per hour during the evening.  Evening
rates are reduced during the evening hours for both hemispheres due to
moonlight.

Pi Puppids  (PPU)     07:08  (107)  -44
Hourly Rate =     0   N. Hemisphere,    <1  S. Hemisphere

Anthelion  (Sagittarids)     14:44  (221)  -15
Hourly Rate =     2   N. Hemisphere,    2  S. Hemisphere

Lyrids (LYR)   17:40  (265)  +34
Hourly Rate =     1   N.  Hemisphere,   <1  S. Hemisphere

Clear Skies!
Robert Lunsford
American Meteor Society



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