Why does the Earth's horizon appear distorted at ISS window edges?

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Bandersnatch
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Hi, new to the forums, nice to meet you folks, etc.

Today the English wikipedia featured a picture of Tracy Caldwell-Dyson in the cupola of ISS(http://en.wikipedia.org/wiki/File:Tracy_Caldwell_Dyson_in_Cupola_ISS.jpg).
In that picture the arc of Earth/space boundary is visibly distorted at the window edges and where the astronaut's forearm obscures the view.
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Looks a bit like capillary action, although it's probably symmetrical and only appears to distort towards one side due to brightness difference around those points.

Anyway, last time I touched optics was in high school, and while I'd love to grok the how&why of the effect, I don't even know where to look for it. Is this due to diffraction? Something else?

It bothers me to no end, and I'd appreciate any help here, be it an in-depth explanation, or just pointing in the right direction.

Cheers chaps.
 

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It's in the camera - you are getting increased contrast at the light-dark boundary. Notice how the cloud detail is also washed out near dark foreground objects?
 
I don't know the reason. But if you just put your finger in front of one of your eye. You will see the similar effect.
Most likely it is diffraction effect. yes...