Does anyone know about this phenomenon? My friend Benson Farb, under the charming misimpression that I am some sort of astronomer, sent me the following image, taken by his uncle Henry Farkas, MD.
That's the Moon on the right, somewhat overexposed. On the left is another image of the Moon -- substantially dimmer. So what is going on?
Consulting the Google, I was able to find multiple examples of similar phenomena, but no explicit explanation: see here, here, here, here, here, here. My first guess was that we were glimpsing a giant Death Star that had been hiding behind the Moon, but upon further thought I regretfully concluded that it's unlikely we would have alien invaders clever enough to build a Death Star but sloppy enough to reveal it prematurely like that.
Actually there is only one sensible explanation: some sort of lensing/reflection phenomenon that is giving rise to multiple images. The two obvious culprits would be the camera lens itself, or the atmosphere. But Henry took the picture in the first place because he saw the ghost image with his naked eyes, so the camera lens is out. Atmosphere it is! This is somewhat corroborated by the fact that different exposures show different separations between the images -- something that could be explained by changing atmospheric conditions.
The atmosphere, whose layers can have very different humidity and temperature, can be a very effective reflector and refractor. Here is an image of a "sun pillar," to show how dramatic the effects can be.
So I'm pretty convinced that the atmosphere is to blame. On the other hand, it's a little funny that the images aren't vertically aligned, which is what I would naively expect. And this wouldn't be the first time that my lack of real-world knowledge steered me dramatically wrong. Anyone familiar with this phenomenon?
