L37: Bailly

Bailly is a libration object located close to the southwestern limb of the moon. Traditionally it has been recognized as the largest crater on the nearside of the moon, but today it seems to have been upgraded to a lunar basin (without the defining maria).

The short description in Charles Wood’s Lunar 100 list states that it is a “barely discernible basin”, and that might be so, but as a crater I found it both rewarding and quite straightforward. My observations was done under a 13.7 days old moon, which, in combination with the libration at the time, positioned the terminator on top of Bailly’s far wall, thus creating a nice framing of the view.

At first I was a bit confused by the shadow on the crater floor in front of the far wall — it seemed to be on the wrong side of the wall. My best guess is that this is an effect either of the moon’s curvature and the closeness to the limb, or of a convex shape of the floor as such. The effect is beautifully illustrated in an image captured under similar lighting conditions by Damian Perch (scroll down to B).

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Sketch made on 26 September 2015, UT 20:30, using a SkyWatcher 10″ and a TeleVue Nagler 3-6 mm zoom. Seeing 4/5. South is up.

The three parallel strokes above Bailly B (the large floor crater to the left in the sketch) also got me wondering. I have a wage memory of putting them there intentionally, but now a week later they seem odd, to say the least. Again comparing with Peach’s image, I can’t see any structures that might correspond to my strokes. Better just forget about them.

Anyway, I found Bailly a very rewarding object, and I definitely need to return one day.

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