The aim of this study is to delineate the theoretical and methodological principles of two pioneering attempts to solve the longitude problem in the Atlantic Ocean, in the light of available documentation. As the great transoceanic voyages began, between the end of the XV century and Cook’s time, the problem of accurate measurement of longitude at sea, on long voyages out of sight of land, became crucial and its astronomical solution highly desirable. Vespucci adopted the “lunar distance” method, while Verrazzano’s method was based on the observation of the elevation of the sun.
However, despite some inaccuracy, the two Italian navigators succeeded in
identifying correct theoretical principles, providing a fundamental contribution to
the solution of the longitude problem. This was solved many years later, thanks to more accurate astronomical data and careful observation.