(meteorobs) Meteor Activity Outlook for April 25-May 1, 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 part of 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 reaches its new phase on Saturday April 25. At
this time the moon lies close to the sun and is not visible at night. Later
in the period the waxing crescent moon will enter the evening sky but will
not interfere with meteor 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 25/26. 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 07:22 (111) -45. This area of
the sky is located in southern Puppis, close to 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 occurred on April 23 so
current rates are expected to be low, far less than one shower member 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 15:12 (228) -18. This
area of the sky lies in central Libra, two degrees north of the faint star
Iota 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,
extreme eastern Hydra, or western Scorpius 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
reached one on April 16th and remain at or slightly above this level through
April 27. The Lyrids peaked on Wednesday April 22 so current rates are
falling and probably near one shower member per hour this weekend. The
radiant currently lies at 18:20 (275) +34. This area of the sky is located
in western Lyra, five 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. 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 21:04 (316) +43. This area of the sky is located in northeastern Cygnus,
very close to the fourth magnitude star Xi Cygni. Maximum activity occurs on
April 27 so current rates are expected to be near 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.

The Eta Aquariids (ETA) are particles from Halley's Comet, produced in
Earth-crossing orbits many centuries ago. We pass closest to these orbits
from May 5 through the 9th. During this period the Eta Aquariids are at
their best, capable of producing ZHR's of sixty. The actual visible rates
are most often less than half this figure due to the low altitude of the
radiant at dawn. Observed hourly rates at maximum normally vary from zero at
60 degrees north latitude to 25 near the equator and back down to near zero
again in Antarctica, where the radiant elevation is very low. Hourly rates
are now anywhere from zero to two per hour depending on your latitude and
observing conditions. The radiant is currently located at 21:52 (328) -05.
This area of the sky is located in western Aquarius, four degrees west 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. No matter your location these meteors will
appear from the eastern sky and shoot in all directions. If the radiant has
sufficient altitude Eta Aquariid meteors can also be seen shooting down
toward the eastern horizon. With an entry velocity of 68 kilometers per
second, a majority of these meteors will appear to move swiftly with a high
percentage of the bright meteors leaving persistent trains.

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 list 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) - 07:22 (111) -45   Velocity - 18km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - <1

Antihelion (ANT) - 15:12 (228) -18    Velocity - 30km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - 2

Lyrids (LYR) - 18:20 (275) +34    Velocity - 46km/sec.
Hourly Rates - Northern Hemisphere 1 - Southern Hemisphere - <1

Xi Cygnids (XCG) - 21:04 (316) +43    Velocity - 44km/sec.
Hourly Rates - Northern Hemisphere <1 - Southern Hemisphere - <1

Eta Aquariids (ETA) - 21:52 (328) -05     Velocity - 68km/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