(meteorobs) Meteor Activity Outlook for June 2-8, 2006

[Robert Lunsford]

During June observers in the northern hemisphere see some of their lowest
rates of the year. During this month the sporadic rates bottom out producing
an average of only one meteor every ten minutes, even from dark sky sites.
The active showers are also modest this month, barely adding any more
activity to the nighttime scene. Observers south of the equator are enjoying
some of their best rates of the year. This activity is produced from strong
sporadic rates and the fact that the Antihelion radiant is positioned well
south of the celestial equator this time of year. Combine this activity with
long nights and the core of the Milky Way riding high in the sky, and you
get an impressive scene. Unfortunately we have so few southern observers to
enjoy this scenario. This is a reason that observations from south of the
equator are so important. The short nights in the northern hemisphere often
make June the least active month for meteor observers. Those who live in the
more temperate latitudes should make every effort to view the elusive June
activity and to report their valuable data.

This week the moon will reach its first quarter phase on Saturday June 3rd.
At this time the moon will set near 0100 local daylight saving time,
allowing the more active morning hours to be free of interfering moonlight.
As the week progresses the waxing gibbous moon will remain in the sky most
of the night, limiting the window that one may view under optimum
conditions. The estimated total hourly rates for evening observers this week
is near two for observers in the northern hemisphere and three for those
south of the equator. For morning observers the estimated total hourly rates
should be near eight for those in the northern hemisphere and eighteen for
those south of the equator. 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.
Evening rates are reduced due to moonlight.

The radiant positions listed below are exact for Saturday night/Sunday
morning June 3/4. 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. 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 Tau Herculids (THE) are produced by comet 73P/Schwassmann-Wachmann ,
which is currently making headlines as it passed close to the Earth. This
shower was once included in many shower lists. As our understanding of the
shower dynamics increased with this shower it became apparent that this
shower is visible only on rare occasions when the Earth passes through the
trails of debris produce by this comet. Therefore the Tau Herculids have
been removed from most lists and are only rarely discussed. With the close
approach of 73P/Schwassmann-Wachmann to the Earth in 2006, there exists the
small possibility that some activity may be seen from this shower during the
first week of June. The Earth already passed the node of the comet on May 31
so no strong activity is expected. A few stragglers are not out of the
question though. Using the IMO's shower parameters listed at:
http://www.imo.net/files/data/vmdb/vmdbrad.txt, I have calculated that the
radiant for this shower will be located near 15:12 (228) +40 this weekend.
This area of the sky is located in northeastern Bootes, three degrees west
of the third magnitude star Beta Bootis. The actual radiant of shower
members may differ significantly due to the fragmentation of this comet and
the very slow entry velocity. The best time to view possible activity is
near midnight when the radiant lies highest in the sky. This shower is well
placed for viewing in the northern hemisphere as it passes through the
zenith for those located at 40N latitude. At extreme northern latitudes the
length of the night is shortened appreciably, limiting the time one can view
activity. As one progresses southward the length of night increases but the
radiant altitude decreases. South of the equator the radiant altitude
becomes a major factor, reducing the possibility of seeing any activity from
this source. The radiant does not rise above the horizon south of 50S
latitude. With an entry velocity of only 15 kilometers per second, these
meteors will appear to move slowly, helping to aid in their identification.
A great majority of these meteors will possess an angular velocity less than
5 degrees per second with the highest possible angular velocity certainly
being less than 10 degrees per second. Please report any positive sightings
to the AMS, the IMO News list, or Meteorobs as soon as possible after your
observation.

The Antihelion (ANT) radiant is now centered at 17:44 (266) -23. This area
of the sky is located on the Ophiuchus/Sagittarius border, five degrees
northeast of the third magnitude star Theta Ophiuchi. This radiant is best
placed near 0200 local daylight time when it lies on the meridian and is
highest in the sky. Rates at this time should be near two per hour for those
north of the equator and three per hour south of the equator. With an entry
velocity of 30 km/sec., the average Antihelion meteor would be of
medium-slow speed.

The Daytime Arietids (DAR) are active from a radiant located approximately
thirty degrees 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 02:52 (043) +21, which is located
in central Aries ten degrees southeast of the second magnitude star Hamal
(Alpha Arietis). This shower peaks on June 7 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 are now at their annual
minimum activity. One would expect to see perhaps six random meteors per
hour during the last hours before dawn from rural observing sites. During
the evening hours perhaps two random meteors can be seen per hour. Sporadic
rates seen from the southern hemisphere are now increasing toward a
secondary maximum in July. One would see approximately fifteen random
meteors per hour during the late morning hours and three per hour during the
evening. These morning rates may appear a bit inflated but keen observers
under pristine skies can easily verify an average of one random meteor every
four minutes. Of course those viewing from less than optimal conditions will
witness much less activity.

Tau Herculids (THE)   15:16 (228) +40
Northern Hemisphere >1 - Southern Hemisphere 0

Antihelion (ANT)   17:44 (266) -23
Northern Hemisphere 2 - Southern Hemisphere 3

Daytime Arietids (DAR)   02:52 (043) +21
Northern Hemisphere >1 - Southern Hemisphere 0

*For a detailed explanation on the different classes of meteor showers and
other astronomical terms, please visit:
http://www.amsmeteors.org/showers.html#X2006

Clear Skies!
Robert Lunsford
American Meteor Society