Ferdinand Magellan in the context of "Strait of Magellan"

Spherical Earth or Earth's curvature refers to the approximation of the figure of the Earth as a sphere. The earliest documented mention of the concept dates from around the 5th century BC, when it appears in the writings of Greek philosophers. In the 3rd century BC, Hellenistic astronomy established the roughly spherical shape of Earth as a physical fact and calculated the Earth's circumference. This knowledge was gradually adopted throughout the Old World during Late Antiquity and the Middle Ages, displacing earlier beliefs in a flat Earth. A practical demonstration of Earth's sphericity was achieved by Ferdinand Magellan and Juan Sebastián Elcano's circumnavigation (1519–1522).

The realization that the figure of the Earth is more accurately described as an ellipsoid dates to the 17th century, as described by Isaac Newton in Principia. In the early 19th century, the flattening of the earth ellipsoid was determined to be of the order of 1/300 (Delambre, Everest). The modern value as determined by the US DoD World Geodetic System since the 1960s is close to 1/298.25. The scientific study of the shape of the Earth is known as geodesy.

Today the term South Seas, or South Sea, most commonly refers to the portion of the Pacific Ocean south of the equator. The term South Sea may also be used synonymously for Oceania, or even more narrowly for Polynesia or the Polynesian Triangle, an area bounded by the Hawaiian Islands, New Zealand and Easter Island. Pacific Islanders are commonly referred to as South Sea Islanders, particularly in Australia.

The term was coined as Mar de Sur, or "South Sea",  by Spanish conquistador Vasco Núñez de Balboa in 1513 as he it encountered on the southern coast of the Isthmus of Panama and it was applied to the entirety today's Pacific Ocean. In 1520, Ferdinand Magellan named the same ocean the Pacific Ocean, and over time Magellan's name became more well-known.

Guam (/ˈɡwɑːm/ GWAHM; Chamorro: Guåhan [ˈɡʷɑhɑn]) is an island that is an organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. Guam's capital is Hagåtña, and the most populous village is Dededo. It is the westernmost point and territory of the United States, as measured from the geographic center of the U.S. In Oceania, Guam is the largest and southernmost of the Mariana Islands and the largest island in Micronesia. In 2022, its population was 168,801. Chamorros are its largest ethnic group, but a minority on the multiethnic island. The territory spans 210 square miles (540 km; 130,000 acres) and has a population density of 775 per square mile (299/km).

Indigenous Guamanians are the Chamorro, who are related to the Austronesian peoples of the Malay Archipelago, the Philippines, Taiwan, and Polynesia. Unlike most of its neighbors, the Chamorro language is not classified as a Micronesian or Polynesian language. Like Palauan, it possibly constitutes an independent branch of the Malayo-Polynesian language family. The Chamorro people settled Guam and the Mariana islands approximately 3,500 years ago. Portuguese explorer Ferdinand Magellan, while in the service of Spain, was the first European to visit and claim the island in March 1521. Guam was fully colonized by Spain in 1668. Between the 17th and 19th centuries, Guam was an important stopover for Spanish Manila galleons. During the Spanish–American War, the United States captured Guam in June 1898. Under the 1898 Treaty of Paris, Spain ceded Guam to the U.S. effective April 11, 1899.

Alonso de Arellano was a 16th-century Spanish explorer who commanded one ship that was part of the fleet that re-discovered the Philippines after the Magellan and López de Villalobos expeditions.

Samar (/ˈsɑːmɑːr/ SAH-mar) is the third largest island in the Philippines, with a total population of 1,924,651 as of the 2024 census. It is located in the eastern Visayas and its main language and ethnicity is Waray while its main religion is Roman Catholic. Since 1965, the island is divided into three provinces: Western Samar, Northern Samar, and Eastern Samar. The capitals of these provinces are, respectively, Catarman, Catbalogan, and Borongan., all part of the Eastern Visayas region. In commemoration of the establishment of these provinces, June 19 is celebrated as an annual holiday. The island was first sighted by Ferdinand Magellan on March 16, 1521. Although he did not land, other expeditions were made. Many names, such as Samal, Ibabao, and Tandaya, were given to the island prior to the arrival of the Spaniards in 1596. During the early days of Spanish occupation, Samar was under the jurisdiction of Cebu. In the Philippine–American War, Eugenio Daza led a successful attack against the United States Army, later called the Balangiga massacre. This attack led to the Pacification of Samar and deaths of 2,000 people.

In the American colonization of the Philippines, two uprisings were created; the former was the Pulajan movement which caused massacres in the country. The Battle off Samar was held off the island. In the martial law under Ferdinand Marcos, the Sag-od massacre was caused. After the martial law, the island still has the New People's Army rebellion. Samar is the easternmost island in the Visayas archipelago. The island lies to the northeast of Leyte and lies to the southeast of the Bicol Peninsula on Luzon. To the west is the Samar Sea, and to the north and east of Samar lies the Philippine Sea. The island has the Samar Island Natural Park and has numerous biological discoveries and forests.

The Magellan expedition (10 August or 20 September 1519 – 6 September 1522) was the first voyage around the world in human history. It was a Spanish expedition that sailed from Seville in 1519 under the initial command of Ferdinand Magellan, a Portuguese sailor, and completed in 1522 by Spanish Basque navigator Juan Sebastián Elcano.

The initial goal of the voyage was to secure time to explore the possibility of a southwestern passage around South America to China and the Spice Islands (now part of Indonesia). After crossing the Atlantic, wintering in Patagonia, and suppressing a mutiny, the expedition found and transited the Straits of Magellan in 1520. After crossing the Pacific Ocean to the Philippines, Magellan was killed during a raid on the Mactan chief Lapulapu in 1521. The ship Victoria under Juan Sebastian Elcano—who began the expedition as a boatswain— took command of the expedition and sailed into the open Indian Ocean, avoided landing in South Africa despite the resulting starvation, and bluffed his way into resupply at the Cape Verde Islands before completing the first circumnavigation on 6 September 1522. Of the initial 270 crew members, only 18 sailors completed the entire journey.

Explorers are listed below with their common names, countries of origin (modern and former), centuries of activity and main areas of exploration.

The Magellan expedition, sometimes termed the Magellan–Elcano expedition, was a 16th-century Spanish expedition planned and led by Portuguese explorer Ferdinand Magellan. Its purpose was to secure a maritime trade route with the Moluccas, or Spice Islands, in present-day Indonesia. The expedition departed Spain in 1519 and returned there in 1522 under the command of Spanish navigator Juan Sebastián Elcano, who completed the voyage after Magellan's death in the Philippines. One of the most significant voyages in the Age of Discovery, the nearly three-year expedition totaled 60,440 km (37,560 mi) and achieved the first circumnavigation of Earth in history. It also marked the first crossing of the Pacific by a European expedition, revealing the vast scale of that ocean, and proved that ships could sail around the world on a western sea route.

The five-ship fleet left Spain on 20 September 1519 with about 270 men. After crossing the Atlantic Ocean, the ships continued south along the eastern coast of South America. Entering the Strait of Magellan on 1 November 1520, the fleet passed through to the Pacific Ocean, which Magellan himself named Mar Pacifico. The fleet crossed the Pacific in 98 days, stopped in Guam and the Philippines, and successfully reached the Moluccas in November 1521. A much-depleted crew led by Elcano finally returned to Spain on 6 September 1522, having sailed west across the Indian Ocean, around the Cape of Good Hope through waters controlled by the Portuguese, and north along the west African coast to finally arrive in Spain.