Question: when did the Portuguese explore the gold coast of the area that the island classified as being in by the United Nations?

full_context: Document 1: Portugal: Portugal spearheaded European exploration of the world and the Age of Discovery. Prince Henry the Navigator, son of King João I, became the main sponsor and patron of this endeavour. During this period, Portugal explored the Atlantic Ocean, discovering several Atlantic archipelagos like the Azores, Madeira, and Cape Verde, explored the African coast, colonized selected areas of Africa, discovered an eastern route to India via the Cape of Good Hope, discovered Brazil, explored the Indian Ocean, established trading routes throughout most of southern Asia, and sent the first direct European maritime trade and diplomatic missions to China and Japan.
Document 2: Saint Helena: Saint Helena is one of the most remote islands in the world, has one commercial airport under construction, and travel to the island is by ship only. A large military airfield is located on Ascension Island, with two Friday flights to RAF Brize Norton, England (as from September 2010). These RAF flights offer a limited number of seats to civilians.
Document 3: Portuguese discovery of the sea route to India: One of the sailors, Bartolomeu Dias passed the southernmost point of Africa known as the Cape of Good Hope in 1488. He declared it possible to travel to India by going around Africa. The Portuguese were then able to make an immense profit by using their own ships to retrieve the spices.
Document 4: Portuguese discoveries: Portuguese discoveries (Portuguese: Descobrimentos portugueses) are the numerous territories and maritime routes discovered by the Portuguese as a result of their intensive maritime exploration during the 15th and 16th centuries. Portuguese sailors were at the vanguard of European overseas exploration, discovering and mapping the coasts of Africa, Canada, Asia and Brazil, in what became known as the Age of Discovery. Methodical expeditions started in 1419 along West Africa's coast under the sponsorship of prince Henry the Navigator, with Bartolomeu Dias reaching the Cape of Good Hope and entering the Indian Ocean in 1488. Ten years later, in 1498, Vasco da Gama led the first fleet around Africa to India, arriving in Calicut and starting a maritime route from Portugal to India. Portuguese explorations then proceeded to southeast Asia, where they reached Japan in 1542, forty - four years after their first arrival in India. In 1500, the Portuguese nobleman Pedro Álvares Cabral became the first European to discover Brazil.
Document 5: Saint Helena: The island was uninhabited when discovered by the Portuguese in 1502. One of the most remote islands in the world, it was for centuries an important stopover for ships sailing to Europe from Asia and South Africa. Napoleon was imprisoned there in exile by the British, as were Dinuzulu kaCetshwayo (for leading a Zulu army against British rule) and more than 5,000 Boers taken prisoner during the Second Boer War.
Document 6: History of the Cape Colony before 1806: The written history of the Cape Colony in what is now South Africa began when Portuguese navigator Bartolomeu Dias became the first modern European to round the Cape of Good Hope in 1488. In 1497, Vasco da Gama sailed along the whole coast of South Africa on his way to India, landed at St Helena Bay for 8 days, and made a detailed description of the area. The Portuguese, attracted by the riches of Asia, made no permanent settlement at the Cape Colony. However, the Dutch East India Company (VOC) settled the area as a location where vessels could restock water and provisions.
Document 7: Tristan da Cunha: Tristan da Cunha is part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha. This includes Saint Helena and equatorial Ascension Island some 3,730 kilometres (2,318 mi) to the north of Tristan. The island has a population of 267 as of January 2016.
Document 8: Middle Ages: In the early 15th century, the countries of the Iberian peninsula began to sponsor exploration beyond the boundaries of Europe. Prince Henry the Navigator of Portugal (d. 1460) sent expeditions that discovered the Canary Islands, the Azores, and Cape Verde during his lifetime. After his death, exploration continued; Bartolomeu Dias (d. 1500) went around the Cape of Good Hope in 1486 and Vasco da Gama (d. 1524) sailed around Africa to India in 1498. The combined Spanish monarchies of Castile and Aragon sponsored the voyage of exploration by Christopher Columbus (d. 1506) in 1492 that discovered the Americas. The English crown under Henry VII sponsored the voyage of John Cabot (d. 1498) in 1497, which landed on Cape Breton Island.
Document 9: Saint Helena: Located in the South Atlantic Ocean on the Mid-Atlantic Ridge, more than 2,000 kilometres (1,200 mi) from the nearest major landmass, Saint Helena is one of the most remote places in the world. The nearest port on the continent is Namibe in southern Angola, and the nearest international airport the Quatro de Fevereiro Airport of Angola's capital Luanda; connections to Cape Town in South Africa are used for most shipping needs, such as the mail boat that serves the island, the RMS St Helena. The island is associated with two other isolated islands in the southern Atlantic, also British territories: Ascension Island about 1,300 kilometres (810 mi) due northwest in more equatorial waters and Tristan da Cunha, which is well outside the tropics 2,430 kilometres (1,510 mi) to the south. The island is situated in the Western Hemisphere and has the same longitude as Cornwall in the United Kingdom. Despite its remote location, it is classified as being in West Africa by the United Nations.
Document 10: Saint Helena: The ship RMS Saint Helena runs between St Helena and Cape Town on a 5-day voyage, also visiting Ascension Island and Walvis Bay, and occasionally voyaging north to Tenerife and Portland, UK. It berths in James Bay, St Helena approximately thirty times per year. The RMS Saint Helena was due for decommissioning in 2010. However, its service life has been extended indefinitely until the airport is completed.
Document 11: Saint Helena: A satellite ground station with a 7.6-metre (25 ft) satellite dish installed in 1989 at The Briars is the only international connection providing satellite links through Intelsat 707 to Ascension island and the United Kingdom. Since all international telephone and internet communications are relying on this single satellite link both internet and telephone service are subject to sun outages.
Document 12: Spice trade: The first country to attempt to circumnavigate Africa was Portugal, which had, since the early 15th century, begun to explore northern Africa under Henry the Navigator. Emboldened by these early successes and eyeing a lucrative monopoly on a possible sea route to the Indies the Portuguese first crossed the Cape of Good Hope in 1488 on an expedition led by Bartolomeu Dias. Just nine years later in 1497 on the orders of Manuel I of Portugal, four vessels under the command of navigator Vasco da Gama rounded the Cape of Good Hope, continuing to the eastern coast of Africa to Malindi to sail across the Indian Ocean to Calicut, on the Malabar Coast. in south India -- the capital of the local Zamorin rulers. The wealth of the Indies was now open for the Europeans to explore; the Portuguese Empire was the earliest European seaborne empire to grow from the spice trade.
Document 13: European exploration of Africa: European exploration of Sub-Saharan Africa begins with the Age of Discovery in the 15th century, pioneered by Portugal under Henry the Navigator. The Cape of Good Hope was first reached by Bartolomeu Dias on 12 March 1488, opening the important sea route to India and the Far East, but European exploration of Africa itself remained very limited during the 16th and 17th centuries. The European powers were content to establish trading posts along the coast while they were actively exploring and colonizing the New World. Exploration of the interior of Africa was thus mostly left to the Arab slave traders, who in tandem with the Muslim conquest of the Sudan established far - reaching networks and supported the economy of a number of Sahelian kingdoms during the 15th to 18th centuries.
Document 14: European colonisation of Southeast Asia: The spice trade was made possible by the maritime trade route. In 1498, the Portuguese navigator, Vasco da Gama, sailed round the Cape of Good Hope and opened up a sea route from Europe to India. Bringing home samples of exotic oriental products, da Gama greatly increased European interest in the new trade route and the new trade route quickly facilitated the expansion of trade. Eventually, the Dutch wrestled control of it from the Portuguese in the 17th century, and in the 18th century, the British gained control of it from the Dutch. Nevertheless, the spice route greatly increased trading activities, deepened the economic relations between Europe and Southeast Asia and as a result, more European merchants found their way to Southeast Asia.
Document 15: Saint Helena: Saint Helena (/ˌseɪnt həˈliːnə/ SAYNT-hə-LEE-nə) is a volcanic tropical island in the South Atlantic Ocean, 4,000 kilometres (2,500 mi) east of Rio de Janeiro and 1,950 kilometres (1,210 mi) west of the Cunene River, which marks the border between Namibia and Angola in southwestern Africa. It is part of the British Overseas Territory of Saint Helena, Ascension and Tristan da Cunha. Saint Helena measures about 16 by 8 kilometres (10 by 5 mi) and has a population of 4,255 (2008 census). It was named after Saint Helena of Constantinople.
ground_truth: 15th century
sub_queries: What area is the island classified as being in by the United Nations? Answer: West Africa
when did the portuguese explore the gold coast of West Africa Answer: 15th century