Saint Helena (/ˌseɪnt həˈliːnə/ SAYNT-hə-LEE-nə) is a tropical island of volcanic origin in the South Atlantic Ocean, 4000 km east of Rio de Janeiro. It is part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha, which also includes Ascension Island and the islands of Tristan da Cunha. Saint Helena measures about 16 by 8 kilometres (10 by 5 mi) and has a population of 4,255 (2008 census).