The process of determining a vehicle’s position and directing its movement is called navigation. The word navigation comes from two Latin words-navis, meaning “ship,” and agere, meaning “to drive.” The explorers of the 1500s sailed with only a few simple technological aids to guide them. However, with these, along with the stars and the Sun, they navigated the oceans of the world. They could plot and hold a course, measure their progress, and estimate their position in relation to land. Astrolabes, usually made of brass or iron, were widely used in the Middle Ages by astronomers to plot the position of the Sun and other celestial bodies. In the 1400s, sailors began using the technology of astrolabes to determine the latitude of their ships. A sailor would sight a star along the bar shown in the photograph. Then, by aligning the bar with markings engraved on the disk of the astrolabe, he could determine the latitude. The astrolabe became obsolete with the invention of the sextant, an instrument navigators use to measure the angular distance between two points such as the horizon and the Sun.
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