Just watched a really interesting 'science show' (I love living in NY with how many cool 'niche' tv shows are on tv), anyway the thing that I learned is that Borealis are caused by weaknesses in the earths electromagnetic shield.
Because the earth shield is weakest at the poles this is why they are seen in the northern/southern most parts of the earth.
What was also interesting is that because of the continued weakening we could see borealis as far as the equator, of course is this happens we'll all be fried with deadly cosmic rays from the sun but at least it will be pretty.
P.S. Something else I learned is that polarity (eg compasses pointing north - swaps about once every 800,000 years).