January 5, 2012
image by Harald Paleske, Langendorf, Germany
Note: While working on a future Sky & Telescope Exploring the Moon column I came across this excellent LPOD from Aug 16, 2008 that is well worth revisting. In the comments in the 2008 LPOD Danny Caes pointed out that the crater behind Drygalski on the left is Ashbrook at 112°W longitude. I've not seen a better image.
Beyond Bailly, almost (85° W longitude) on the mean limb, is a large crater that is infrequently seen. With a diameter of 149 (or 163 km according to IAU and Rükl, respectively), Drygalski is ~50% larger than Copernicus. The only nearside craters with a relatively fresh classical Copernican look that are bigger are nearby Hausen (167 km) and distant Humboldt (207 km) and Petavius (177 km). Why are these big craters near the limb? Harald's large scale image of Drygalski shows the smooth floor, and hints at the rougher floor behind the central peak. A terrace is visible on the left wall but the right wall seems more disorganized, probably because of the larger number of craters that cut that side, visible both here and in the Lunar Orbiter IV view.
2008-07-26, 4:42 UT. 408mm Newton f 8, 5 m, DMK 1/30sec. exposure, red filter, stack of 300 frames, 3 picture mosaic; seeing good (7/10)
Rükl plates 72 & VI
Harald's excellent Solar (with Moon coming) website
Yesterday's LPOD: Quiet Crisium
Tomorrow's LPOD: Where They Are