Lydia
Site Admin
Posted:
Thu Mar 23, 2006 2:00 pm
Joined: 03 Feb 2004
Posts: 601
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Observers Needed!
Please read Mr. Dunham's request.
LL
As most of you know by now, Early Saturday evening, April 1st,
the thin crescent Moon, 19% sunlit, will be passing through the
Pleiades star cluster. This may be the best Pleiades passage for
eastern North America since a similar one on March 23, 1969;
actually, this one will be a little better, with the Moon a slightly
thinner crescent than then and passing more centrally over the
cluster. It will be an interesting spectacle for anyone with
binoculars to see and thus could be used, with proper publicity, to
generate interest in astronomy in our region, as well as other parts
of the eastern U.S.A. and eastern Canada. Anyone with a camcorder
could even obtain scientifically useful recordings of the numerous
occultations that will occur. A view of the Moon in the Pleiades,
with tracks for the center of the Moon for some major cities, is on
p. 61 of the April issue of Sky and Telescope.
Predictions of the total occultations of the brighter stars for
hundreds of cities and towns are on the main IOTA Web site at
http://www.lunar-occultations.com/iota . Only predictions for the
brighter stars are given there; elsewhere on that site, there are
predictions for 40 North American cities with data for some more
events. But more detailed predictions have been computed for many
observers that I will be distributing as part of the package of
predictions for all 2006 occultations described in a message that I
distributed near the beginning of the year to most of you - if you
get it, rename the ".zap" file to ".zip", unzip it, and find your
total lunar occultation predictions, including the Pleiades stars,
for your location in a file called aoccnxxx.006 where xxx is your
station number in the northeastern USA "A region" (if you are in the
n.e. USA, Ontario, or s. Quebec). With large telescopes, you'll be
able to time dozens of occultations; in 1969, Tom Van Flandern timed
60 events using the 26-inch refractor at the U. S. Naval Observatory.
Both the Web Master of the main IOTA site and I will be out of town
from Friday March 24 to March 31 (when I'll be back) for the total
solar eclipse on March 29. So from now until the passage, those
needing total occultation predictions computed for their location
can obtain them upon request (send coordinates to at least 1'
accuracy, or the street address of the observing site) to Derek
Breit, e-mail address breit_ideas@hotmail.com .
There will be several opportunities to observe grazing
occultations within paths about a mile wide at the northern limits
of the regions of visibility of these occultations. In these narrow
zones, the star will appear to move along a tangent line to the
Moon's disk, and will disappear and reappear several times among the
mountains and craters on the dark side of the Moon near the cusp at
the Moon's north pole. Later I will try to add a Moon figure
showing the view. If you are north of the graze zone, the Moon will
narrowly miss the star and there will be no occultation. If you are
south of it, the star will disappear on the dark side, then several
minutes later will reappear on the bright side of the Moon. You can
get some idea of what a grazing occultation of a bright star looks
like by looking at short video clips of a grazing occultation of
Aldebaran recorded in Poland a few years ago. The part before
central graze is at http://iota.jhuapl.edu/Vstup.mpeg and the part
after central graze is at http://iota.jhuapl.edu/Vystup.mpeg .
The star remained hidden behind the Moon for about a minute between
the two sequences. Simple methods for timing and/or video recording
occultations are described at http://iota.jhuapl.edu/timng920.htm .
Charlie Ridgway has posted path overlays on interactive maps
that use google maps to give very detailed map and aerial vies of
graze zones as well as of asteroidal occultations.
His general site at
http://charlie.ridgway.com/Astronomy/Occultations/ has links to the
map sites and describes how to "navigate" the maps to get very
detailed views of regions of interest. There is a link specifically
for the 2006 Pleiades grazes at
http://charlie.ridgway.com/Astronomy/Occultations/06/Grazes/M45.html
On that site, scroll down to April for the April 1/2 Pleiades
passage. This includes three maps showing the paths of all of the
grazes of stars of mag. 7.5 or brighter in three different broad
regions. Then under it are links to the pages/interactive maps for
each of over a dozen grazing occultations that cross the eastern
U.S.A. and southeastern Canada. These are northern-limit grazes that
will occur on the Moon's dark limb except for the grazes of Merope,
Alcyone, Atlas, and Pleione, which are southern-limit grazes on the
Moon's sunlit side. The bright-limb events involving Alcyone can be
observed with small telescopes, and that star is even bright enough
that it can be observed in daylight, so the path is extended west in
the area from southern Arizona to central Texas where it will occur
before sunset. The bright-limb grazes of Merope, Atlas, and
especially Pleione will be quite difficult to observe.
Ridgway has the offsets set properly to show the multiple
events graze zone between the two gray lines. Actually, these
offsets do vary along the paths some; they were determined for the
New York City area for Celaeno; for the Washington, DC area for
Maia; and for Statesboro, GA for Taygeta. The longitudes for the
graze zone offsets for the other grazes on Ridgway's Web site are as
follows:
West
Star Longitude
deg.
Electra - ZC 537 52
SAO 76152 75
Merope - ZC 545 95
Alcyone - ZC 552 95
22 Tau - ZC 543 81
ZC 546 64
ZC 548 83
ZC 553 70
ZC 557 73
Atlas - ZC 560 78
Pleione - ZC 561 79
ZC 562 73
SAO 76234 76
SAO 76249 63
SAO 76259 76
The graze zone offsets will not change significantly for at least 2
deg. of longitude from the above locations, and for most, the valid
range is much larger. Later I will describe here how the offsets
change at other locations along the path so that you can manually
enter the offsets for your area to get the best map of your local
graze zone.
Of special interest are the grazes of the bright 4th-mag. stars Maia
and Taygeta; both stars are close spectroscopic binaries that might
be resolved during these grazes. The path for the graze of Maia
starts near sunset in eastern Iowa, with the twilight getting darker
for good visibility across Ohio (near Lima and north of Columbus),
and especially spectacular in a rather dark sky across northern West
Virginia and the Washington, DC area to Ocean City, Maryland.
Information about expeditions in Ohio and the Washington, DC area,
with many static detailed maps of the latter area, are on my Web
site for the event at http://iota.jhuapl.edu/maia.htm . It's the
best graze in the DC region since the 1969 Pleiades passage, easily
seen with binoculars and some camcorders directly, so the rare event
is worth a special effort.
Similarly, the path for the spectacular graze of Taygeta passes over
the southern part of Birmingham, Alabama; over Macon and Statesboro,
Georgia; and over Hilton Head Is., SC. Harold Povenmire and Becky
Lowder are organizing a large expedition to observe the graze near
Statesboro, GA; if you can, please try to join that effort and let
Becky know at lowderb@yahoo.com .
David Dunham
phones cell 301-526-5590; office 240-228-5609; home 301-474-4722
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