ascension island is an isolated volcanic island, 7°56' south of the equator in the south atlantic ocean. it is about from the coast of africa and from the coast of brazil. 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 to the southeast. the territory also includes the sparsely-populated tristan da cunha archipelago, some to the south, about halfway to the antarctic circle.