I've seen the northern lights once, at a cabin weekend in Wisconsin a couple of years ago. It's a strange thing to experience, especially at that latitude, where the lights aren't as in-your-face as this photo. For the first minute or so, you kind of wonder whether you're hallucinating. Then you realize that everybody else is standing perfectly still and silent, staring at the exact same point in the sky.
This time-lapse video (you'll have to follow the link to watch) shows a far more spectacular display over the Ringebu Fjell in southern Norway, captured by photographer Bernd Proschold. The moment when the clouds clear away, and the lights burst into view is absolutely breathtaking.
The World At Night: A Glimpse of the Far North
(Thanks, Chris Combs!)