The word "Arctic" comes from the ancient Greek Arktikos, or "country of the great bear." Though the Greeks had no knowledge of the polar bear, they named the region after the constellation Ursus Major, the Great Bear, found in the Northern Sky. The Arctic is a region that stays black and fiercely cold for months on end. In the High Arctic, the sun sets in October and does not rise again until late February.

Polar bears are well-adapted to the region's fiercely cold weather. Winter temperatures in the Arctic often plunge to -40 degrees or -50 degrees F and can stay that way for days or even weeks. In January and February, the average temperature in the High Arctic is -29 degrees F.

A thick layer of blubber (up to 4.5 inches thick) provides polar bears with such excellent insulation that their body temperature and metabolic rate remain the same even at -34 degrees F. Polar bears have two layers of fur for further protection from the cold. Compact ears and small tail also help prevent heat loss. A polar bear's body temperature is 98.6 degrees F, which is average for mammals.

On bitterly cold days with fierce winds, polar bears dig out a shelter in a snow bank and curl up in a tight ball to wait out the storm. When curled up in a ball, polar bears sometimes cover their muzzles — which radiate heat — with one of their thickly furred paws.

Polar bears have more problems with overheating than they do with cold. Even in very cold weather, they quickly overheat when they try to run.

Polar bears generally walk at a leisurely pace to keep from overheating. When a Norwegian scientist, Nils Oritsland, studied a polar bear on a treadmill, he found that his subject would move off for short periods of time at higher speeds and would sometimes lie down and refuse to walk at all!