Yesterday, on a very clear and dark evening (in SW France), my wife spotted something unusual in the night sky -- a double image of the crescent moon. I saw the same thing. (And no, neither of us had been drinking.) Other objects, such as distant trees and buildings, all appeared as normal, single images.
When I looked at the moon through binoculars, the double image was the same. But when I looked through just one eyepiece, the moon appeared as a single image.
Foolishly, I didn't take a photo, but it was something like this:
What was going on? Some sort of refraction, perhaps?