A mysterious light

I photographed this "light" thrue the window of the ferry from Stockholm to Helsinki last night. I used shutter speed of 30 second, the target was in the distance so I had to crop a lot an did heavy post processing to change the colours.
For the future this is at least a document of a time when airplanes could not fly due to volcanic eruption in Iceland. So this cannot be anything flying.

And actually it really is another ship that was in the distance.