(meteorobs) Meteor Activity Outlook for June 25-July 1, 2004

[Robert Lunsford]

The moon reaches its first quarter phase on Friday June 25. At this time the
moon lies ninety degrees east of the sun and will set near 0100 local
daylight or summer time. This weekend the waxing half moon will set in the
early morning hours allowing a few hours of viewing under dark skies. The
estimated total hourly rates for evening observers this week should be near
two for those in the Northern Hemisphere and three for those observers south
of the equator. For morning observers the estimated total hourly rates
should be near eight for those located in the Northern Hemisphere and
fifteen for those in the Southern Hemisphere. Evening rates are reduced due
to moonlight. 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 listed below are exact for Saturday night/Sunday
morning June 26/27. The radiant 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 libraries) 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 location. 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 last rise later in the night. This list also
provides the order of ascending velocity for each radiant with those listed
first usually being much slower than those last on the list. Velocity should
not be the prime factor for shower association as all showers can produce
slow meteors. Slow meteors can be produced from normally swift showers, such
as the Leonids, when meteors appear near the radiant or close to the
horizon. The true velocity is only revealed in shower members seen far from
the radiant and high in the sky.

After a mild outburst on June 23, the June Bootids are still active
producing 2-3 meteors each hour from dark sky sites. Another opportunity for
slightly enhanced rates may occur on June 26th near 0100 universal time.
This timing favors the east coast of North America and the northwestern
Atlantic region. Unfortunately the bright gibbous moon will obscure the
fainter meteors. Europe and northwestern Africa will not suffer from the
moonlight at this time but their radiant elevation will be significantly
lower. The radiant is located at 14:56 (224) +47. This area of the sky is
located in northern Bootes some fifteen degrees southeast of Alkaid (Eta
Ursae Majoris), the last star in the handle of the "Big Dipper". Due to the
northern declination this shower is well seen only from the southern
equatorial areas northward to the northern temperate areas. Those located
north of 50 degrees north latitude will have difficulty seeing any activity
due to the very short nights experienced in those latitudes this time of
year. This area of the sky is best placed as soon as it gets dark during the
evening hours. At 18 km/sec. any June Bootids will appear to move quite
slowly compared to most meteors. Again, please make viewing this radiant a
priority this week!

The Theta Ophiuchids (TOP) reach maximum activity on the
27th with very low rates. The radiant is currently located at 16:36
(249) -11. This area of the sky is located in southwestern Ophiuchus, two
degrees southwest of the third magnitude star Zeta Ophiuchi. Due to the
southern declination this shower is well seen only from the northern
temperate areas southward. Even from favored locations ZHR's rarely surpass
2. This area of the sky is best placed near 2300 (11pm local daylight time)
when the radiant lies on the meridian and highest in the sky. At 27 km/sec.
the Theta Ophiuchids are slow compared to most other showers.

The Anthelion radiant is now centered at 19:20 (290) -22. This area of the
sky is located in eastern Sagittarius, two degrees southeast of the third
magnitude star Pi Sagittarii. Since this radiant is large and diffuse, any
slow to medium speed meteor from Sagittarius, southwestern Aquila, western
Capricornus or Scutum could be a candidate for this shower. The center of
this area is best placed near 0100 local standard time when it lies on the
meridian and is highest in the sky. At this time expect to see one shower
member per hour north of the equator and three per hour for those situated
south of the equator.

Unlike most of the annual showers the antihelion source is produced by
debris from unknown objects orbiting in a direct motion like the earth.
These objects are most likely asteroids, which produce stony and metallic
debris whose density is much greater than material produced by comets. This
material collides with the earth on the inbound portion of its orbit, before
its closest approach to the sun. Therefore we best see them just after
midnight when we are facing the direction from which this activity appears.
The antihelion source is active all year from an area of the sky nearly
opposite that of the sun. The center of this source will move approximately
one degree eastward per day and travels through many different
constellations over the course of a year. It may make sense to list these
meteors as anthelions or "ANT" but a majority of meteor organizations prefer
that you list them from the constellation in which the radiant is currently
located or the constellation where the shower reaches maximum activity.
Those who send their data to the International Meteor Organization should
call these meteors Sagittarids (SAG).

The Tau Aquarids (TAQ) are listed among the radiants of the Dutch Meteor
Society. They reach maximum activity on the 27th with an estimated ZHR of 3.
The radiant is currently located at 22:48 (342) -12, which places it in
central Aquarius, one degree west of the fourth magnitude star Tau 2
Aquarii. Southern observers are favored for this shower as the radiant rises
higher into their sky before the onset of morning twilight. These meteors
are best seen just before the start of morning twilight. At 63km/sec. the
majority of Tau Aquarids appear quite swift.

The Northern Apex radiant is now centered at 00:20 (005) +17. This position
lies in southeastern Pegasus, two degrees north of the third magnitude star
Algenib (Gamma Pegasi). This area of the sky is best placed for viewing
during the last dark hour before dawn when it lies highest in the sky. Since
this radiant is large and diffuse, any meteor from southwestern Andromeda,
northwestern Cetus, western Pisces or eastern Pegasus could be a candidate
from this source. Rates would be now close to two per hour regardless of
your location.

Like the antihelion area, both apex areas are active all year long and
travel approximately one degree eastward per day. Unlike the antihelion
debris, these particles orbit the sun in a retrograde motion opposite that
of the earth and are most likely produced by unknown comets. They strike the
earth after their closest approach to the sun. Since they are moving in
opposite directions these particles strike the earth at tremendous
velocities often creating bright meteors with persistent trains. These
particles strike the earth on the morning side of earth and are best seen
just before morning twilight while the sky is still perfectly dark. This is
not really a "shower" per se, but an artificial radiant created by the
Earth's motion through space. Meteors from both branches are normally
included in the sporadic count. I feel it is a worthy project to see if it
is possible to distinguish these meteors from the normal sporadic
background. On rare occasions there are meteors with a zero inclination that
radiate precisely from the apex point on the ecliptic, exactly 90 degrees
west of the sun. In simplistic terms, these meteors are seldom seen since
the Earth "sweeps clean" much of the material that shares the same orbit as
our planet. Much more material is located just north and south of the
earth's orbit with slightly higher or lower inclinations. This creates the
northern and southern branches of the apex activity.

The Southern Apex source lies exactly 30 degrees south of its northern
counterpart at 00:20 (005) -13. This position lies in western Cetus, three
degrees south of the fourth magnitude star Iota Ceti. Like the northern
apex, these meteors are best seen toward dawn when the radiant lies highest
above the horizon in a dark sky. Since this radiant is also large and
diffuse, any meteor from eastern Aquarius, Cetus, or northern Sculptor could
be a candidate from this source. Rates would now be one per hour in the
Northern Hemisphere and two per hour in the Southern Hemisphere.

The Tau Cetids (CET) are also listed among the radiants of the Dutch Meteor
Society. They reach maximum activity on the 27th with an estimated ZHR of 4.
The radiant is currently located at 01:36 (024) -12, which places it in
central Cetus, four degrees southwest of the 4th magnitude star Zeta Ceti.
Once again southern observers are favored for this shower as the radiant
rises higher into their sky before the onset of morning twilight. These
meteors are best seen just before the start of morning twilight. At
66km/sec. the majority of Tau Cetids appear quite swift. Be careful when
trying to distinguish between the Tau Cetids, Southern Apex and the Tau
Aquarids. These three radiants are relatively close in the sky and produce
similar appearing, swift meteors.

The Sporadic rates for the Northern Hemisphere have reached their nadir. One
would currently expect to see perhaps four random meteors per hour during
the last hours before dawn from rural observing sites. This estimate and the
morning estimate for the Southern Hemisphere do not include the apex meteors
listed above. During the evening hours perhaps one random meteor can be seen
per hour from the Northern Hemisphere. Rates seen from the Southern
Hemisphere are now stronger than those seen in the northern skies with
perhaps six random meteors being seen per hour during the early morning
hours and two per hour during the evening. Evening rates are reduced due to
moonlight.

Clear Skies!
Robert Lunsford
AMS Operations Manager