Bailly and the terminator

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Bill Leatherbarrow

Hi David,

The NASA app Dial-a-Moon, when set for the hour of your observation, replicates what you saw exactly. I attach a crop from what it throws up. If you don’t know the website (which is excellent) you can find it at

I think the key to understanding the impression you gained is that the terminator bisects the floor of the crater, leaving the curve of the far wall catching the light beyond the terminator and producing the impression of a raised hump.

Hope this helps