One of the great things about living in high latitudes is the chance to watch the Aurora (Northern lights). The classic shimmering curtains of light are caused by the ionization of particles in the Earth's upper atmosphere by solar winds. In high latitudes (c. 70 degrees) activity is going on most of the time and all you need is darkness and a clear sky. To see the Northern Lights a bit further south in somewhere like Bergen (c. 60 degrees) requires an increase in solar activity associated with coroneal mass ejections (CME) more commonly known as sunspots. Wikipedia has a great article here so I won't go into it in to much detail.
There are a couple of excellent websites that can help you predict when you are there will be increases in solar activity and when that should relate to northern lights where you are.
NOAA is probably the best with good basic info for the general public and lots of more detailed stuff for nerdy folk. I had a great intro lecture from John T on how to use the various graphs etc the other evening when we were out.
Spaceweather.com also has some good forecasts for auroras, meteors etc. and this site from the Univeristy of Alaska in Fairbanks also offers a good prediction and some very nice maps. There is a really good intro to photographing the Lights here.
All of this did not help us (John T, Emma, Oli and myself) when we headed out to Øygarden last week to photography what was predicted to be the best activity in months. We find a great spot, there was very little light polution, the sky was fairly clear and the predictions were good.
We saw nothing! But we did learn that the sun takes a VERY long time to set even in August.
I guess that is something to look forward to in the winter.
The sun takes a very long time to set in the northern hemisphere in August
And even when it did, there was no Northern Lights, just a few wispy clouds :-(