The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth. The tropics are also referred to as the tropical zone and the torrid zone (see geographical zone). The tropics include all the areas on the Earth where the Sun reaches a point directly overhead at least once during the solar year. About 40 percent of the world's human population lives within the tropical zone (by 2008 statistics), and by 2060, 60% of the human population will be in the tropics, owing to high birth rates and migration.