Lunar
Transit through the Pleiades on 2007 December 21
and
Favourable Grazing Occultations in Germany
Dear observer,
on Friday
evening, December 21th, the moon will pass in front of the north-western part of
the Pleiades cluster, causing several grazing occultations throughout Europe. The limit lines of Celaeno (16 Tauri,
5.5mag) and Maia (20 Tauri, 3.9 mag) will run across Central Europe.
The limit
lines intersect outside the extreme western coast of the Bretagne. Nevertheless
the lunar profile allows to combine both events within a limited region.
Organized Expeditions in Germany
Throughout
Germany no such twin observation is possible. Therefore you may join one of two
IOTA/ES expeditions:
- Wolfgang Rothe organizes an expedition to
the graze of Celaeno near the
A13 exit Calau, about midway between Berlin and Dresden combination.
Please see invitation and data sheet here
Path coordinates, times of central graze, elevation correction, and position angles are tabulated here
- The author will organize another expedition
to the graze of Maia about 20
km north of Wiesbaden in the Taunus range, near A3 exit Bad Camberg.
Please see invitation and data sheet here
Path coordinates, times of central graze, elevation correction, and position angles are tabulated here
Position Angle and Profile for Celaeno
The graze of Celaeno takes place in a Cassini area of
the lunar profile. Therefore the historical profile data by Watts (red dashed) are
uncertain. Former graze observations indicate a profile depicted by the green
line. Despite an unsatisfactory scatter of these data the green line is much
more confident.
IMPORTANT: If you observe from the theoretical linimt
line, you probably will see a passage of the star without any occultation. The profile
suggests to choose an observation site at least 1 to 1.5 km north of the
predicted line. A strip up to 4 km north is favorable.
Please
observe at least +/- 3 minutes around the time of central graze tabulated for
your geographical position.
Position Angle and Profile for Maia
Path
The graze of Maia takes place in a Cassini area of the
lunar profile. Therefore the historical profile data by Watts (red dashed) are uncertain.
Former graze observations indicate a profile depicted by the green line. Despite
an unsatisfactory scatter of these data the green line is much more confident.
IMPORTANT: If you observe from the theoretical linimt
line, you certainly will see a passage of the star without any occultation. The
profile suggests to choose an observation site at least 2 km north of the
predicted line. A strip up to 4 km north is favorable.
Please
observe at least +/- 3 minutes around the time of central graze tabulated for
your geographical position.
Grazing
occultations help to improve the precise knowledge about the polar limb
profiles of the moon. This is necessary to evaluate Baily's bead observations
during solar eclipses for the determination of the sun’s diameter. Appearances
and disappearances of beads are essential events, therefore probing the depth
of valleys during grazing occultations is especially important.
Maps for Germany
The following
maps show the limit lines for both grazing occultations across Germany allowing
a rough orientation. Please take detailed path data and the times of central
graze from tables linked in chapter “Organized Expeditions in Germany”. Do not
forget to take into account the offset suggested in the preceeding chapter.
Additionally
an adjustment for terrain elevation may be required in mountain ranges.
With sufficient accuracy you can calculate this parallel southward offset by
multiplying the elevation of you observation site with a factor of 0.62.
Transit through Pleiades Cluster
Anywhere
else you may observe several regular or so-called total occultations of
Pleiades stars, or you may just enjoy the transit. This overview, strictly valid
for central Germany, gives you an impression what you will see:
Clear skies
and successful observation!
Alfons Gabel
International Occultation Timing Association / European Section