I really love this card! :) First of all, because I've been interested in geography since early childhood :) It's always been interesting for me, why in the Northern- and Southernmost parts of Earth the night can last even half a year :) Of coruse, now I just understand it, but still, I think it's something worth seeing, not just understanding.
Here's the information about the Arctic Circle from the back side of this card:
The Arctic Circle - A border where the sun does not sink in the summer nor rise in the winter on its northern side - for at least one day a year. While quietly proceeding, the Arctic Circle fluctuates during its journey of 250 kilometres one or two meters every day - swinging back and forth, but nevertheless reaching each end alonf the way at interims of 40 000 years.