Saint Helena is a British Overseas Territory consisting of Saint Helena and Ascension Islands, and the island group of Tristan da Cunha.

Saint Helena: Uninhabited when first discovered by the Portuguese in 1502, Saint Helena was garrisoned by the British during the 17th century. It acquired fame as the place of Napoleon BONAPARTE's exile from 1815 until his death in 1821, but its importance as a port of call declined after the opening of the Suez Canal in 1869. During the Anglo-Boer War in South Africa, several thousand Boer prisoners were confined on the island between 1900 and 1903.;

Saint Helena is one of the most remote populated places in the world. The British Government committed to building an airport on Saint Helena in 2005. After more than a decade of delays and construction, a commercial air service to South Africa via Namibia was inaugurated in October of 2017. The weekly service to Saint Helena from Johannesburg via Windhoek in Namibia takes just over six hours (including the refueling stop in Windhoek) and replaces the mail ship that had made a five-day journey to the island every three weeks.;

Ascension Island: This barren and uninhabited island was discovered and named by the Portuguese in 1503. The British garrisoned the island in 1815 to prevent a rescue of Napoleon from Saint Helena. It served as a provisioning station for the Royal Navy's West Africa Squadron on anti-slavery patrol. The island remained under Admiralty control until 1922, when it became a dependency of Saint Helena. During World War II, the UK permitted the US to construct an airfield on Ascension in support of transatlantic flights to Africa and anti-submarine operations in the South Atlantic. In the 1960s the island became an important space tracking station for the US. In 1982, Ascension was an essential staging area for British forces during the Falklands War. It remains a critical refueling point in the air-bridge from the UK to the South Atlantic.;

The island hosts one of four dedicated ground antennas that assist in the operation of the Global Positioning System (GPS) navigation system (the others are on Diego Garcia (British Indian Ocean Territory), Kwajalein (Marshall Islands), and at Cape Canaveral, Florida (US)). NASA and the US Air Force also operate a Meter-Class Autonomous Telescope (MCAT) on Ascension as part of the deep space surveillance system for tracking orbital debris, which can be a hazard to spacecraft and astronauts.

Tristan da Cunha: The island group consists of Tristan da Cunha, Nightingale, Inaccessible, and Gough Islands. Tristan da Cunha, named after its Portuguese discoverer (1506), was garrisoned by the British in 1816 to prevent any attempt to rescue Napoleon from Saint Helena. Gough and Inaccessible Islands have been designated World Heritage Sites. South Africa leases a site for a meteorological station on Gough Island.

Saint Helena: 15 57 S, 5 42 W;

Ascension Island: 7 57 S, 14 22 W;

Tristan da Cunha island group: 37 15 S, 12 30 W

Saint Helena: tropical marine; mild, tempered by trade winds;

Ascension Island: tropical marine; mild, semi-arid;

Tristan da Cunha: temperate marine; mild, tempered by trade winds (tends to be cooler than Saint Helena)

the islands of this group are of volcanic origin associated with the Atlantic Mid-Ocean Ridge

Saint Helena: rugged, volcanic; small scattered plateaus and plains;

Ascension: surface covered by lava flows and cinder cones of 44 dormant volcanoes; terrain rises to the east;

Tristan da Cunha: sheer cliffs line the coastline of the nearly circular island; the flanks of the central volcanic peak are deeply dissected; narrow coastal plain lies between The Peak and the coastal cliffs

active volcanism on Tristan da Cunha

volcanism: the island volcanoes of Tristan da Cunha (2,060 m) and Nightingale Island (365 m) experience volcanic activity; Tristan da Cunha erupted in 1962 and Nightingale in 2004

The vast majority of the population of Saint Helena, Ascension, and Tristan da Cunha live on Saint Helena. Ascension has no indigenous or permanent residents and is inhabited only by persons contracted to work on the island (mainly with the UK and US military or in the space and communications industries) or their dependents, while Tristan da Cunha – the main island in a small archipelago – has fewer than 300 residents. The population of Saint Helena consists of the descendants of 17th century British sailors and settlers from the East India Company, African slaves, and indentured servants and laborers from India, Indonesia, and China. Most of the population of Ascension are Saint Helenians, Britons, and Americans, while that of Tristan da Cunha descends from shipwrecked sailors and Saint Helenians.

Change in Saint Helena’s population size is driven by net outward migration. Since the 1980s, Saint Helena’s population steadily has shrunk and aged as the birth rate has decreased and many working-age residents left for better opportunities elsewhere. The restoration of British citizenship in 2002 accelerated family emigration; from 1998 to 2008 alone, population declined by about 20%.

In the last few years, population has experienced some temporary growth, as foreigners and returning Saint Helenians, have come to build an international airport, but numbers are beginning to fade as the project reaches completion and workers depart. In the long term, once the airport is fully operational, increased access to the remote island has the potential to boost tourism and fishing, provide more jobs for Saint Helenians domestically, and could encourage some ex-patriots to return home. In the meantime, however, Saint Helena, Ascension, and Tristan da Cunha have to contend with the needs of an aging population. The elderly population of the islands has risen from an estimated 9.4% in 1998 to 20.4% in 2016.

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