Meteor Activity Outlook for April 30-May 6, 2011

May is a fairly slow month for meteor activity. The Eta Aquariids are very
active the first two weeks of the month then fade as the month progresses. The
only other showers active this month are the weak Nu Cygnids, the Eta Lyrids,
and the Antihelion radiant. These will add only 1-2 meteors per hour to the
total count. 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)
are strong but beginning to decline.

During this period the moon reaches its new phase on Tuesday May 3. At this time
the moon will lie near the sun and will not be visible at night. Toward the end
of this period a waxing crescent moon will enter the evening sky but will not
interfere with observing. The estimated total hourly rates for evening observers
this week is near three as seen from the northern hemisphere and four as seen
from the southern hemisphere. For morning observers the estimated total hourly
rates should be near fourteen from the northern hemisphere and twenty as seen
from south of the equator. 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 (the area of the sky where meteors appear
to shoot from) positions and rates listed below are exact for Saturday night/Sunday
morning April 30/May 1. 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 wide Antihelion (ANT) radiant is now centered at 15:32 (233) -19. This area
of the sky lies in eastern Libra, eight degrees northwest of the second
magnitude star Dschubba (Delta Scorpii). This radiant is best placed near 0200
local daylight time (LDT) when it lies on the meridian and is located highest in
the sky. Due to the large size of this radiant, any meteor radiating from
extreme eastern Hydra, Libra, northern Lupus, or western Scorpius could be a
candidate for this shower. Rates at this time should be near two per hour as
seen from the northern hemisphere and three per hour as seen from south of the
equator. With an entry velocity of 30 km/sec., the average Antihelion meteor
would be of medium-slow speed.

The team of Sirko Molau and Juergen Rendtel have discovered a weak radiant
active at this time in the constellation of Cygnus. Video data shows that the Nu
Cygnids (NCY) are active from April 18th through May 7th. Maximum activity
occurred on the morning of April 20th. The radiant is currently located at 21:40
(325) +47. This position lies in northeastern Cygnus, just north of the faint
star known as Rho Cygni. The radiant is best placed during the last dark hour
before dawn, when it lies highest above the horizon in a dark sky. At 42km/sec.
the Nu Cygnids would produce meteors of medium velocity. Expected rates are less
than one per hour. Due to the northerly declination of the radiant, these
meteors are not well seen from south of the equator.

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 30 near the equator and back down to near zero again in Antarctica,
where the radiant elevation is very low. Hourly rates this weekend are anywhere
from zero to five per hour depending on your latitude and observing conditions.
Rates will increase significantly as the week progresses as we approach the May
7 maximum. The radiant is currently located at 22:20 (335) -03. This area of the
sky is located in northern Aquarius, just south of the fourth magnitude star
Gamma Aquarii. The best time to view this activity is during the hour 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
67 kilometers per second, a majority of these meteors will appear to move
swiftly with a high percentage of the bright meteors leaving persistent trains.
Surprisingly, this shower produces very few fireballs.

As seen from the mid-northern hemisphere (45N) one would expect to see
approximately nine 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
fourteen 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 condensed version of the expected activity this week.
Rates and positions are exact for Saturday night/Sunday morning.