If we are now going to report of the visibility of the Northern Lights,
so here you have the situation in southern-parts of Finland (which is
pretty much more in the North than the areas where Celts actually lived
-I would say).
Although in Finnish Lapland Northern Lights are pretty common, we see
them seldom here in the southern parts. I personally remeber only about
10-15 times during the last 10 years or so (pretty impressive they were
-although nothing compared to the light show you experience in Lapland).
However, it should be remembered that the glow from city-lights might
have pretty often hidden Northern lights from the view (at least they do
it for, e.g., the Milky Way) - and naturally the winter nights are
usually pretty cloudy. Moreover, no Northern Lights are visible in the
summer time, as it doesn't get dark enough. Still, I would say that NL
must be considered pretty rare even here.
Dept. of the Study of Religions
University of Helsingfors