These days, a smartphone with a Global Positioning System app can generally pinpoint your location on the globe to within about 20 feet [11], but for most of human history, it was far too easy to get lost. The problem of navigation was particularly acute on the open sea. Although determining a ship’s latitude could be easily derived from the position of the sun relative to the horizon, determining longitude was a much harder problem—because of the earth’s rotation, the sun’s east/west coordinates are not fixed in the heavens.
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