Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around 1,600 kilometres (1,000 mi) from the coast of Africa and 2,250 kilometres (1,400 mi) from the coast of Brazil, which is roughly midway between the horn of South America and Africa. It is governed as part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha, of which the main island, Saint Helena, is around 1,300 kilometres (800 mi) to the southeast. The territory also includes the sparsely populated Tristan da Cunha archipelago, some 3,730 kilometres (2,300 mi) to the south, about halfway to the Antarctic Circle.