February 8, 2013

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Among the Astrophysicists

image by Jocelyn Serot, France

Gérard Coute and I were both in the garden on the evening on Jan 25th to take advantage of a long expected clear night. As an echo to his mosaic of the NW limb area, here's a close-up view of the Eddington-Struve-Russell region. Eddington is a flooded crater very similar to Fracastorius. It was tilted - possibly if a putative Procellarum basin subsided - and subsequent lavas entered its arena, almost completely burying its SE rim. On its floor a pair of facing parentheses are all that remain of the small crater Eddington P. On the north part of the floor a faint line is just visible. This line was also on an image taken by Claude Navarro. Is it a rille or a low angle fault (a kind of a smaller scale, less straight, Straight Wall)? Behind Eddington are the two big overlapping craters, Struve and Russell (170 and 103 km diam, resp.). It's difficult to tell which one formed first because the same lava that flooded Eddington also almost completely filled both of them. There are some clues, however. First, the rim of Struve looks a bit more battered. The western part also looks lower, but we must take the perspective effect into account. Second the floor of Russell looks smoother, with fewer impact craters. The floor of Struve also shows some low ridges (which, incidently, and for an unknown reason, seem all oriented NS) whereas Russell looks flat as a mirror. But we could also speculate that the lavas filling Russell are younger. So the initial question remains open. What's your guess?

Jocelyn Serot

Note by CAW: I mercilessly enhanced Jocelyn's image (a slice is to the right) to bring out the faint line he mentioned in Eddington, which is labelled #2, and another one labelled #3. Also visible is a slightly curved line (#1) on the floor of Struve. These look like rilles, and the LRO Quickmap confirms it - #1 and #2 and 3, each slightly less than 1 km wide. There is a subtle dome on the floor of Russell, but I was unable to determine its height with the QuickMap Path tool. The LRO QuickMap shows that the rim of Eddington overlaps Struve, and while no overlap is clear, the rim of Russell is better preserved than that of Eddy, so Russell appears to be the younger crater as Jocelyn surmised. Finally, the low ridges on Struve may be due to the lighter hued, and slightly elevated older lavas seen on QuickMap.

Technical Details
2013-01-25, 22h57 UT. 12" Dall-Kirkham refl at prime focus (F=5m). IR685 filter. DMK31. Processing : Autostakkert2
(300 frames/4000) + Registax 6.

Related Links
Rükl plate 17
21st Century Atlas chart 28.

Yesterday's LPOD: Albumen Moon

Tomorrow's LPOD: Unequal Ejecta


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