Well Played, Mauer

February 29, 1504:

 Christopher Columbus uses his knowledge of a lunar eclipse that night to convince Native Americans to provide him with supplies. For a year Columbus and his men remained stranded on Jamaica. A Spaniard, Diego Mendez, and some natives paddled a canoe to get help from Hispaniola. That island's governor, Nicolás de Ovando y Cáceres, detested Columbus and obstructed all efforts to rescue him and his men. In the meantime Columbus, in a desperate effort to induce the natives to continue provisioning him and his hungry men, successfully won the favor of the natives by correctly predicting a lunar eclipse for 29 February 1504, using the Ephemeris of the German astronomer Regiomontanus. Help finally arrived, no thanks to the governor, on 29 June 1504, and Columbus and his men arrived in Sanlúcar, Spain, on 7 November.

Wasn't that trick used in A Connecticut Yankee In King Arthur's Court?  I guess Twain just borrowed from history.