(meteorobs) Meteor Activity Outlook for April 13-19, 2007

Robert Lunsford lunro.imo.usa at cox.net
Fri Apr 13 11:13:00 EDT 2007


April has one major annual shower and the start of another. The Lyrids are
active from April 16-25 and reach maximum activity on the 22nd. While not
the strongest annual shower they produce much better rates than has been
seen for the past three months. The Eta Aquarids also reach a ZHR of one on
April 19 and slowly continue to increase in strength as the month
progresses. Sporadic rates seen in the northern hemisphere are actually
worse than those seen in March. This trend will continue through June. On
the other hand rates seen from the southern hemisphere are increasing toward
a July maximum.

During this period the moon reaches its new phase on Tuesday April 17. At
this time the moon will rise and set with the sun and will not interfere
with observing during this period. The estimated total hourly rates for
evening observers this week is near two for those north of the equator and
three for observers south of the equator. For morning observers the
estimated total hourly rates should be near nine for northern observers and
fifteen for those south of the equator. 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 14/15. 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. It must be remembered that meteor activity is
rarely seen at the radiant position. Rather they shoot outwards from the
radiant so it is best to center your field of view so that the radiant lies
at the edge and not the center. Doing this will allow you to easily trace
the path of each meteor back to the radiant (if it is a shower member) or in
another direction if it is a sporadic. 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.

The Antihelion (ANT) radiant is now centered at 14:32 (218) -15. This area
of the sky is centered in western Libra, five degrees northwest of the third
magnitude star Zubenelgenubi (Alpha Librae). This radiant is best placed
near 0200 LDT when it lies on the meridian and is highest in the sky. Rates
at this time should be near one per hour as seen in the northern hemisphere
and two per hour for those located south of the equator. With an entry
velocity of 30 km/sec., the average Antihelion meteor would be of
medium-slow speed.

The Lyrids (LYR) are the first major annual shower of the season. ZHR's
reach one on April 16th and remain at or slightly above this level through
April 25. According to the IMO, peak rates will occur on Sunday April 22
near 22:30 Universal Time. This timing favors Asia where local observers
will actually see the best rates on the morning of April 23. For North
America this time corresponds to 6:30 PM EDT and 3:30 PM PDT on April 22,
which of course is during daylight. Peak Lyrid rates seen from North America
should be similar on both the mornings of the 22nd and 23rd. ZHR's average
eighteen but raw visual rates can vary from 5-25, depending on your
observing conditions. The radiant currently lies at 17:32 (263) +34. This
area of the sky is located in central Hercules, four degrees southeast of
the third magnitude star Pi Herculis. 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 radiant elevations only a
small fraction of the Lyrid activity can be seen. 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.

Sporadic rates are slowing decreasing for observers in the northern
hemisphere and slightly rising for those south of the equator. One would
expect to see perhaps seven random meteors during the last hour before dawn
from rural observing sites located in the northern hemisphere. During the
first dark hour after the end of evening twilight, perhaps two random
meteors can be seen per hour. Sporadic rates increase as the night
progresses so rates seen near midnight would be near four per hour. Late
morning sporadic rates seen from the southern hemisphere are now near
thirteen per hour from rural observing sites. During the first dark hour
after the end of evening twilight, perhaps three random meteors can be seen
per hour, increasing to eight by midnight.

Antihelion (ANT) - 14:04 (211) -12
Northern Hemisphere 1 - Southern Hemisphere 2

Lyrids (LYR) 17:32 (263) +34
Northern Hemisphere 1 - Southern Hemisphere <1

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#X2006

Clear Skies!
Robert Lunsford
American Meteor Society



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