(meteorobs) Meteor Activity Outlook for April 20-26, 2007

[Robert Lunsford]

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 first quarter phase on Tuesday April
24. At this time the half illuminated moon will set near 0100 local daylight
time and will not interfere with observing the remainder of the morning. 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 twenty no
matter your location. 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.
Evening rates are reduced due to moonlight.

The radiant positions listed below are exact for Saturday night/Sunday
morning April 21/22. 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 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 will next be at perihelion in March 2008 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 radiant position lies at 07:18 (110) -45. This
area of the sky is located in southern Puppis, two degrees southwest of the
third magnitude star Sigma Puppis. The radiant lies highest in a dark sky as
soon as it becomes dark at the end of evening twilight. Peak activity occurs
on April 23. Away from this night rates are expected to be far 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 (ANT) radiant is now centered at 14:56 (224) -16. This area
of the sky is centered in western Libra, close to 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
reached 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 18:04 (271) +34. This
area of the sky is located in eastern Hercules, eight degrees southwest of
the brilliant zero magnitude star Vega (Alpha Lyrae). 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.

The The Eta Aquarids (ETA) are particles from Halley's Comet, which last
passed through the inner solar system in 1986. Even though this is now over
twenty years ago, material is still encountered every year in late April and
throughout most of May. We pass closest to Halley's orbit on May 6. At that
time Eta Aquarid rates can reach thirty shower members per hour as seen from
the northern tropical areas southward. Current rates would be less than one
per hour from a radiant located at 21:36 (324) -07. This area of the sky is
located in western Aquarius, one degree southeast of the third magnitude
star Sadalsuud (Beta Aquarii). 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 66 kilometers per second, a majority of
these meteors will appear to move swiftly.

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 one 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 two random meteors can be seen
per hour, increasing to eight by midnight. Evening rates are reduced due to
moonlight.

Pi Puppids (PPU)  07:18 (110) -45
Northern Hemisphere - 0   Southern Hemisphere - <1

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

Lyrids (LYR) 17:32 (263) +34
Northern Hemisphere - 10  Southern Hemisphere - 3

Eta Aquarids (ETA)  1:36 (324) -07
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