The Arctic and the Antarctica are the two main cold places on earth. We have decided to concentrate on only the Arctic. Unlike Antarctica, an ice-covered continental plateau surounded by oceans, the Arctic has a central ocean almost surrounded by land. Low precipitation is a characteristic of the Arctic, so large and elaborate lake and river systems are rare. However, permafrost restricts the downward drainage of meltwater from snow, and the water thus accumulates on the surface as shallow lakes, ponds and marshes. Arctic winters are long and cold, with short and cool summers. The Arctic circle marks the border of a zone in which the sun never rises during at least one day in winter and never sets during at least one day in summer. The north pole is not the coldest spot in the Arctic because its climate is moderated by the ocean.