Subject: What causes the green light in the sky.

I read a post in which a scientist answered the question why the sky is blue at 
day and black at night. He also said that if you make a photograph of the sky 
at night, with a long lighting time (or whatever that's called in English) you 
see a green colour. He explained that that's because of reactions 80 km above 
us. So what's going on there? What causes this green light. Or is it yellow 
plus the blue light scattered around?

Re: What causes the green light in the sky.