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Something I do if I think there's activity, and I'm not sure if the glow ia aurora, is take a photo of the northern sky with a digital camera capable of a long exposure (5-15 secs, enough to bring out the stars). Most aurora is a very particular colour of green - if you see that green in the photo, then it's definitely aurora - yellow-orange is probably streetlight glow, blue probably twilight, whitish probably cloud. Your eyes don't see colours well in the dark, so this is a way of removing a little doubt if you're standing around in the cold!
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