Christopher Columbus used his knowledge of lunar cycles to trick natives on San Salvador into giving him food and shelter. They believed he could make the moon disappear forever and cause doom and destruction. Columbus got real lucky and his bluff worked. Maybe you can use the lunar calendar for something less malevolent, like learning the position of the moon so that you can better use your sextant. $1
The quadrant, sextant, and astrolabe wer the most prominent navigation tools of Columbus and the sailors who followed him during the Age of Discovery in the 16th and 17th centuries. When using the quadrant, sailors would locate the North Star with the viewfinder, and a weighted string would align itself with a degree marking telling you the angle between the star and the horizon. The sextant used an adjustable dial, as opposed to string, but ultimately, they all provided a working latitude for sailors. $175
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