(meteorobs) Meteor Activity Outlook for June 11-17, 2004

[Robert Lunsford]

The moon reaches its new phase on Thursday June 17. At this time the moon
lies in conjunction with the sun and will rise and set with the sun.
Therefore it will not be visible in the night sky. This weekend the waning
crescent moon will rise during the early morning hours but will not
interfere with observing as long as you keep it out of your field of view.
The estimated total hourly rates for evening observers this week should be
near two for those in the Northern Hemisphere and three for those south of
the equator. For morning observers the estimated total hourly rates should
be near ten for those located in the Northern Hemisphere and fourteen for
those in the Southern Hemisphere. 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 12/13. 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.

The Omega Scorpids (OSC) appear on the list of DMS radiants. This display
was predicted to peak on June 2 with a ZHR of 5. Current rates would be
lower with a radiant position at 16:40 (250) -21. This position lies in
southwestern Ophiuchus, six degrees northeast of the first magnitude orange
star Antares (Alpha Scorpii). It would be best to watch for this activity
near midnight local daylight time when the radiant lies on the meridian and
is positioned highest in the sky. With an entry velocity of only 21 km/sec.
any activity from this radiant would be extremely slow.  This activity is
best seen from Northern Temperate latitudes southward.

The Anthelion radiant is now centered at 18:24 (276) -23. This area of the
sky is located in northwestern Sagittarius, three degrees northwest of the
third magnitude star Lambda Sagittarii. Since this radiant is large and
diffuse, any slow to medium speed meteor from southeastern Ophiuchus,
northern Sagittarius, southern Serpens Cauda 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 June Lyrids (JLY) / Xi Draconids reach maximum activity in mid-June.
While recent June Lyrid activity has been strong enough to place it back on
the IMO's working list, some of this activity can be attributed to another
radiant exactly twenty degrees north of the June Lyrids. After its discovery
back in 1966, the June Lyrids produced some modest activity for the next
several years. During the early 70's reports of this activity waned as did
interest in this shower. Then after more than two decades of poor activity
two teams of observers in the USA and The Netherlands discovered a sharp
radiant near Draco's head in 1996, active between June 11 and the 17th.
These meteors were much more numerous than the June Lyrids that year and
have continued to provide more activity than its southerly neighbor ever
since. The current radiant positions for the June Lyrids is 18:24 (276) +35
and 18:24 (276) +55 for the Xi Draconids. These positions lie on the in
western Lyra just two degrees southeast of the 4th magnitude star Kappa
Lyrae and in southern Draco, four degrees southeast of the 4th magnitude
star Xi Draconis, the northernmost star in the "Lozenge" (head) of Draco. As
seen from the Northern Hemisphere these radiants lie high in the sky passing
nearly overhead during the short nights that occur this time of year. They
are well placed between 0100 and 0200 when they lie highest above the
horizon. They lie much lower in the sky as seen from the Southern Hemisphere
and are not well seen. Meteors from both radiants are somewhat swift unless
seen near the radiant or low in the sky. Please keep an eye out for this
activity and let us know which radiant is active for you.

The Northern Apex radiant is now centered at 23:24 (351) +12. This position
lies in southern Pegasus, four degrees southeast of the second magnitude
star Mirfak (Alpha 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 northern Aquarius,
northwestern Cetus, western Pisces or southern 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 23:24 (351) -18. This position lies in eastern Aquarius, six
degrees southeast of the third magnitude star Delta Aquarii. 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, western Cetus, northern
Sculptor or eastern Pisces Austrinus 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 Arietids (DAR) are active from a radiant located just west of the sun.
The radiant rises just before the start of morning twilight and any activity
would be seen shooting upwards from the northeastern horizon.  These meteors
are of medium velocity and usually last several seconds as they skim the
outer regions of the earth's atmosphere. The current radiant position is
located at 03:16 (049) +27 which is located in northeastern Aries some five
degrees northwest of the Pleiades star cluster. This shower peaked on June 6
with a ZHR of 60. Even with such strong rates the unfavorable altitude at
the time of daybreak makes seeing this activity a difficult challenge. On
the other hand, those with radio meteor equipment can easily detect this
activity as it is the strongest annual radio meteor shower of the year.

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 two random meteors 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 three per hour during the evening.

Clear Skies!
Robert Lunsford
AMS Operations Manager