The frequency and intensity of northern lights (Aurora borealis) depends on the intensity of the solar winds, which in turn depends on the activity of the sun itself. In a cycle of eleven years, the intensity varies considerably. During times of major activity, polar lights can be seen even in southern parts of Europe. Because solar winds travel for 2-4 days before reaching the earth, you can almost precisely predict a higher chance of northern lights to be seen. For information on solar activity, the
NICT Space Weather Information Center provides a useful website.
The best time to observe them is late autumn/early winter (end of October to mid-December) as well as the end of February until the beginning of April. During these periods, the magnetic field of the sun and the earth are parallel to each other, causing the greatest effect.
As soon as you travel north of the polar circle, you will be able to observe polar lights almost all year around.
Try stay away from any artificial light sources like cities or villages. The light emitted makes it hard to see the subtle nuances in clors and shapes.
On a skiing trip in northern Sweden, above the polar circle in the Sarek National Park, I was able to observe polar lights every other night for almost three weeks at the end of February. It was the most impressive sight and you begin to understand why people in former times believed the northern lights to be the souls of their ancestors.
Enjoy your trip!
Andrew
