Hi,
Welcome to the tricky world of Aurora photography. I beleive you are facing several obstacles - to overcome of course.
1. Are you doing film or digital?
For film there is the reciprocity factor which means that exposure must be increased at long exposre times - not so severe with some modern films. I don't know if digital faces this problem - maybe not - if so shorter exposure time for digital.
2. Aurora varies a lot in intensity - if possible meter it and use that exposure and again double the time - you need varied exposures tpo really get it right. Its tricky with the dark sky and the bright Aurora
3. Dress warmly - as Aurora in the the north is usually seen on cold nights. Might be a problem for digital cameras with lcd screens.
4. I prefer slower films as the faster films might not give you a dark blue sky but a black one. However - experiment with this.
Good luck,
Chilly photos,
Ronald
