Meteor Activity Outlook for April 18-24, 2009

Meteor activity picks up a bit during April as
two major showers are active during the month. The first of these, the Lyrids,
are active from the 16th through the 27th, with a pronounced maximum on the 22nd
and 23rd. The Eta Aquariids start appearing near the 27th and reach maximum activity
during the first week in May. Sporadic rates are low but steady as seen from the
mid-northern hemisphere (45 N). Sporadic rates seen from the mid-southern
hemisphere (45 S) rise this month toward a maximum in July.

During this period the moon wanes from its last
quarter phase down to almost new at the end of this period. The crescent moon will
not interfere with observing as long as you are able to keep it out of your field
of view while observing. The estimated total hourly rates for evening observers
this week is near two as seen from the northern hemisphere and three for those
situated south of the equator. For morning observers the estimated total hourly
rates should be near ten for those located in the mid-northern hemisphere (45 N)
and fifteen for those viewing from the mid-southern hemisphere (45 S). Locations
between these two extremes would see activity between the listed figures. 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 and rates listed below are exact
for Saturday night/Sunday morning April 18/19. 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. Viewing there 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 following showers are expected to be active 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 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 wide Antihelion (ANT) radiant is now centered at 14:44 (221) -16. This
area of the sky lies in western Libra, only two degrees west of the second magnitude
double star Zubenelgenubi (Alpha Librae). This radiant is best placed near 0200 LDT when it
is located on the meridian and lies highest in the sky above the horizon. Due to the
large size of this radiant, any meteor radiating from southeastern Virgo, Libra, or
extreme eastern Hydra could be a candidate for this shower. Rates at this time
should be near two per hour as seen from the southern hemisphere and only one as
seen from north of the equator. With an entry velocity of 30km/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 27. According to the IMO calendar, peak rates will occur on Wednesday April
22 near 11:00 Universal Time. This timing favors the western half of North America
where observers will have the radiant located high in a dark sky, as long as you
are not situated too far north where morning twilight begins to interfere at this
time. Sirko Molau’s video data lists the peak on the 23rd, so observers are
encouraged to observe on both nights if possible. ZHR’s average eighteen but raw
visual rates can vary from 5-25, depending on your observing conditions. The radiant
currently lies at 17:52 (268) +34. This area of the sky is located in eastern
Hercules, twelve 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 46 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 video studies of Sirko Molau have revealed a weak radiant active in Cygnus
this time of year. The Xi Cygnid (XCG) radiant is currently located at
20:20 (305) +40. This area of the sky is located in central Cygnus, only two degrees
west of the second magnitude star Sadr (Gamma Cygni). Maximum activity occurs on
April 27 so current rates are expected to remain less than one per hour. These
meteors are best seen during the last dark hour before dawn, when the radiant
lies highest above the horizon in a dark sky. This shower is best seen from the
northern hemisphere, where the radiant lies high in the sky at dawn. At 44 km/sec.
the Xi Cygnids will usually produce meteors of medium velocity.

As seen from the mid-northern hemisphere (45N) one would expect to see approximately
seven Sporadic meteors per hour during the last hour before dawn as seen
from rural observing sites. Evening rates would be near two per hour. As seen from
the mid-southern hemisphere (45S), morning rates would be near thirteen per hour as
seen from rural observing sites and three per hour during the evening hours. Locations
between these two extremes would see activity between the listed figures.

The table below presents a summary of the expected activity this week. Rates and
positions are exact for Saturday night/Sunday morning but may be used all week.