The Polar Chart of Pedro Reinel (c. 1521–1524): A Diplomatic Tool or a Scientific Argument?

A chart of the sixteenth century is extant, depicting the southern hemisphere and containing the earliest known representation of the southeast coast of South America, in the wake of Magellan and Elcano's circum navigation. In this paper, it is argued that astronomical observations of longitude were accommodated in the representation, and that the chart was produced in the specific context of the Juntas of Badajoz-Elvas, held between the representatives of the Spanish and Portuguese Crowns, to discuss the location and possession of the Spice Islands. It is further shown that the chart was produced using the information brought to Seville by the ship San Antonio, which had deserted the fleet in October 1520, before the passage to the Pacific Ocean was found. It is concluded that this chart presents a unique historical milestone in the history of cartography, containing the earliest material evidence of the effective use of astronomical methods to determine longitude in a nautical context. [ABSTRACT FROM AUTHOR]