Longitude from Solar Eclipses - Magellan and Columbus

Arne B. Molander

Abstract:	Five hundred years ago the determination of useful longitude data from eclipses was usually limited by the lack of accurate timing devices. There were, however, a special class of solar eclipses which could provide accurate longitude measurements using the then available time and angle-measuring instrumentation. These solar eclipses were those extremely rare events where the explorer was able to observe the eclipse maximum near the horizon at the remote longitude – that is, within an hour or so of sunrise or sunset. On 17 April 1520 Ferdinand Magellan is known to have utilized this type of “sunrise” solar eclipse to measure the longitude of South America’s east coast with a high degree of accuracy that has since baffled historians. Although Christopher Columbus left no record of his longitude measurements, he did leave his son Ferdinand a brief written description of a February 1477 voyage in which he claims to have sailed 300 miles beyond “Thule” (Greenland). Coincidentally, on 13 February 1477 there was a unique “sunset” solar eclipse visible 300 miles west of Greenland in the Bay of Fundy, the only Atlantic location having the ice-free 50-foot tides described in the note to his son.
Published in:	Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000) June 26 - 28, 2000 The Catamaran Resort Hotel San Diego, CA
Pages:	495 - 501
Cite this article:	Molander, Arne B., "Longitude from Solar Eclipses - Magellan and Columbus," Proceedings of the IAIN World Congress and the 56th Annual Meeting of The Institute of Navigation (2000), San Diego, CA, June 2000, pp. 495-501.
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