(meteorobs) Meteor Activity Outlook for June 18-24, 2004

Robert Lunsford lunro.imo.usa at cox.net
Thu Jun 17 13:35:21 EDT 2004


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 crescent moon will set near
the end of evening twilight leaving the entire night available of observing.
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. 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 19/20. 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.

Activity from the June Bootids (JBO) is possible next week as the Earth
passes close to the paths of comet P7/Pons-Winnecke created in the early
19th century. Whether any activity will be seen depends on how much debris
remains in orbit and just how close the Earth passes from this debris.
Russian meteor researchers Sergey Shanov and Sergey Dubrovsky predict the
best chance for activity occurs near 1100 Universal Time on June 23. This is
favorable for the west coast of North America westward over the Pacific
Ocean to Japan. While the eastern Pacific region will have a lower radiant
altitude the western Pacific will suffer from moonlight as the waxing
crescent moon will still be above the horizon. The radiant is located at
14:48 (222) +48. 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.
Please make viewing this radiant a priority next week!

The Theta Ophiuchids (TOP) reach maximum activity on the 27th with very low
rates. The radiant is currently located at 16:04 (241) -12. This area of the
sky is located in northwestern Scorpius, very close to the 4th magnitude
star Xi Scorpii. 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 18:52 (283) -23. This area of the
sky is located in central Sagittarius, three degrees north of the second
magnitude star Nunki (Sigma Sagittarii). Since this radiant is large and
diffuse, any slow to medium speed meteor from southeastern Ophiuchus,
Sagittarius, southern Serpens Cauda, 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 22:20 (335) -15, which places it in
western Aquarius, two degrees east of the fourth magnitude star Iota
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 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 18:44 (281) +35
and 18:44 (281) +55 for the Xi Draconids. These positions lie on the in
central Lyra, three degrees southeast of the zero magnitude star Vega (Alpha
Lyrae) and in southern Draco, four degrees northwest of the 4th magnitude
star Kappa Cygni. 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 23:52 (358) +14. This position
lies in southeastern Pegasus, four degrees southwest 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,
northeastern Aquarius, 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 23:52 (358) -16. This position lies in eastern Aquarius close
to the fourth magnitude star Omega 1 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
northeastern 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 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 01:12 (018) -15, which places it in
central Cetus, five degrees south of the 3rd magnitude star Eta 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 3 radiants are relatively close in the sky and produce
similar appearing, swift meteors.

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 03:32 (053) +31 which is located near the intersection of
Aries-Taurus-Perseus, eight 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



More information about the Meteorobs mailing list