The Arctic
The Arctic is defined by three things; geography, the tree line and the temperature. The Arctic Circle is an invisible line of latitude at approximately 66°33′ N, north of this line the sun does not set on the summer soltice, and doesn't rise on the winter solstice. There is also a natural boundary where tree's don't grow because of the cold, combined with areas where the average temperature of the warmest month is below 10°C.
