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

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The usual figures for selenographic colongitude given in an ephemeris are defined with respect to the mean centre of the lunar disk (and so is 90 degrees exactly at exactly first quarter). Owing to libration in longitude, a feature can actually be up to 3.5 degrees either east or west of the terminator at the time when the ephemeris predicts that the feature should be on it. So the usual tabulated figures of selenographic colongitude only give the approximate position of a feature in relation to the terminator. After correcting for libration in longitude it might be that Molesworth really did observe earlier than the time of first appearance of the interior illumination of Plato. I am grateful to Gerald for the additional comments and the copy of his original observing notes and drawing. It is clear that the floor of Plato presents a number of unusual scenarios of light and shade under early sunrise and sunset and that the ephemeris might not tell the whole story in terms of what might be visible at the eyepiece. 6 BAA Lunar Section Circular Vol. 49 No. 4 April 2012
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 7
Page 1 and 2: Director: Bill Leatherbarrow The Br
Page 3 and 4: Topographical notes compiled by Pet
Page 5: Sunrise on Plato Nigel Longshaw In
Page 9 and 10: Join us at our Yahoo! Group: Lunar
Page 11 and 12: Images Since March’s LSC, lunar i
Page 13 and 14: (detail below) BAA Lunar Section Ci
Page 15 and 16: Peter Oden took this detailed image
Page 17 and 18: BAA Lunar Section Circular Vol. 49
Page 19 and 20: Figure 1. A modified sketch of Aris
Page 21 and 22: 2012-Apr-06 UT 00:21-04:04 Ill=99%
Page 23 and 24: Graze occultations ZC 1198 on 2012
Page 25: Lunar data for April 2012, lunation

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

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