(meteorobs) Meteor Activity Outlook for April 25-May 1, 2008

[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 25th, with a pronounced maximum on the 22nd. Unfortunately this
date coincides with a full moon this year so activity will be reduced. The
Eta Aquarids start appearing near the 20th 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 reaches its last quarter phase on Monday April
28th. At this time the moon will be located ninety degrees west of the sun
and will rise near 0100 local daylight time (DST). During this period the
slow evening hours will be free of moonlight while the moon will shine
brightly during the morning hours. Successful meteor observations can be
undertaken if you observe with the moon at your back or toward the darkest
portion of the sky. Dry, transparent skies will help immensely as far less
moonlight will be scattered allowing fainter stars, thus fainter meteors to
be seen. As seen from the mid-northern hemisphere (45 N) the estimated total
hourly rates during the evening observers would be only one. For morning
observers the estimated total hourly rates should be near six. For those
located in the mid-southern hemisphere (45 S) morning rates would be near
ten and evening rates near two. 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. Morning rates are reduced by moonlight.

The radiant positions and rates listed below are exact for Saturday
night/Sunday morning April 26/27. 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 at perihelion this past March but no activity of this shower
has been reported so far. 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 occurred on April
23, but a few shower members may be detected up to April 28. 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 large Antihelion (ANT) radiant is now centered at 15:16 (229) -18. This
area of the sky lies in central Libra, two degrees north of the faint star
Iota Librae. Actually any meteor from western Scorpius, eastern Hydra, as
well as Libra could be a candidate for this shower. This radiant is best
placed near 0200 LDT time when it lies on the meridian and is highest in the
sky. Rates at this time should be near one for northern observers and two
for observers south of the equator. With an entry velocity of 30 km/sec.,
the average Antihelion meteor would be of medium-slow speed.

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 3 through the 7th. 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. Early in the
activity period, as we are now, hourly rates would vary from zero to two per
hour depending on your latitude and observing conditions. The radiant is
currently located at 22:00 (330) -04. This area of the sky is located in
northern Aquarius, four degrees south of the third magnitude star Sadalmelik
(Alpha 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 66 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) the Sporadic rates are low,
but fairly steady. One would expect to see approximately four random meteors
during the last hour before dawn from rural observing sites and only one per
hour during the evening hours. As seen from the mid-southern hemisphere
(45S) morning rates would be near seven per hour as seen from rural
observing sites and two per hour during the evening hours. Morning rates are
reduced due to moonlight.

The table below presents a condensed version of the expected activity this
week. Rates and positions are exact for Saturday night/Sunday morning.

Pi Puppids (PPU)  07:18 (110) -45   Velocity - 18km/sec.
Northern Hemisphere - 0   Southern Hemisphere - <1

Antihelion (ANT) - 15:16 (229) -18   Velocity - 30km/sec.
Northern Hemisphere - 1   Southern Hemisphere - 2

Eta Aquariid (ETA)  22:00 (330) -04   Velocity - 66km/sec.
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#X2008

Clear Skies!
Robert Lunsford
American Meteor Society