(meteorobs) Meteor Activity Outlook for April 18-24, 2009

[Robert Lunsford]

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.

Pi Puppids (PPU) - 07:18 (110) -45    Velocity - 18km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - <1

Antihelion (ANT) - 14:44 (221) -16    Velocity - 30km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - 2

Lyrids (LYR) - 17:52 (268) +34    Velocity - 46km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - <1

Xi Cygnids (XCG) - 20:20 (305) +40    Velocity - 44km/sec.
Hourly Rates - 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#X2009

Clear Skies!
Robert Lunsford
American Meteor Society