Vol 49, No 4, April 2012 - BAA Lunar Section

Encke, 2012 March 03
Peter Grego
Notes: Further to studies of Encke made on 2009
April 5 and 6, an observation was made with the
crater illuminated by an earlier morning Sun. Paul
Stephens’ 9-inch f/11 Newtonian was used—as
the Moon was high, the observation had to be
made atop a pair of wooden stepladders dating
back to the 1930s that had belonged to Paul’s
grandfather. They knew how to make things to
last in those days—neither I nor the ladders
creaked in the slightest. No observational
template was used—this observational drawing is
a PhotoPaint enhanced version of the scanned
original telescopic pencil sketch.
Encke is distinctly polygonal in outline. About
half of the crater’s floor was filled with shadow
cast by its eastern rim. Several north-south ridges
were discerned on Encke’s floor, and the western
floor at the base of the inner western wall was
dark. A kink in the outline of the western rim
marked the brightest part of the crater; this was
the location of the crater Encke N, but it was not
obviously crater-like in this view. The western rim
of Encke cast a serrated shadow to the west, and
is depicted here as it appeared shortly after the
observation was commenced; by the end of the
observation session, however, the shadow had
retreated noticeably eastward but still retained all
the original individual shadow peaks.
The north part of crater Encke H, southwest of
Encke, joined Encke’s shadow; it has been
depicted a little too large here. Broad, complex
ridges run around the eastern side of Encke; these
have not been depicted as accurately as I had
hoped. The ridges form the eastern wall of a larger
crater, Encke T, in which Encke itself lies.
2009 April 5 notes: Shadow was being cast
by the crater’s eastern rim onto Encke’s floor;
illuminated points within the shadow were
located at the 1 o’clock and 5 o’clock
positions. Some floor detail was visible in the
form of a pronounced north-south ridge, with
a smaller scalloped ridge to its northwest. A
little more time would have allowed a more
detailed study of the floor, but deteriorating
transparency prevented this. Encke’s inner
western wall appeared indented in a couple of
places, at around the 9 o’ clock and 11
o’clock positions. Wrinkle ridges ran around
the eastern glacis of Encke, the boldest of
them running to the south of the crater.
BAA Lunar Section Circular Vol. 49 No. 4 April 2012
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