The Arctic and the Antarctic are two of the iciest regions on Earth. They may look similar, but in many ways they are very different. The Arctic, which includes the North Pole, is mostly an ice-covered ocean. The Antarctic, which contains the South Pole, is a land mass largely covered by enormous glaciers. Both regions are about 1.5 times the size of the United States (including Alaska).

Both places are extremely cold yet surprisingly dry. The moisture that does fall usually comes as snow. But in many places there is so little precipitation that if it were rain, you would think of these places as deserts.

In addition to the Arctic Ocean, the Arctic includes many of the surrounding lands, including Greenland, the world's biggest island. It also contains large portions of northern Canada and smaller parts of Alaska, Russia, Norway, and Iceland.

Explorers trying to reach the North Pole must cross treacherous ice floes. Polar bears live on the ice, and travel is difficult because the floes can be separated by open water gaps called leads. Shifting floes can also collide creating icy ridges that can be extremely difficult to cross.

Antarctic explorers face extremely cold temperatures and thin air at altitudes that often climb to 10,000 feet (3,048 meters) above sea level. They also face frigid blasts called katabatic winds that sweep from the interior highlands to the sea. Taken together, these conditions make Antarctica one of the world's harshest climates.