The first compass dates back to the first century B.C., when the Chinese observed that pieces of lodestone, an iron mineral, always pointed north when they were placed on a surface. There is evidence that Arab sailors were using compasses as early as A.D. 600, and as Arab influence spread north into Europe, so did the compass. By the fourteenth century, European ships carried maps that were charted with compass readings to reach different destinations. Portugal’s Prince Henry (1394–1460), also called Henry the Navigator, advanced the use of compasses in navigation by encouraging sailors and mapmakers to coordinate their information to make more accurate maps of the seas. Also in the fifteenth century, an important observation was made by none other than Genoese navigator and explorer from Spain Christopher Columbus (1451–1506), who noticed that as he sailed to the New World, his compass did not align directly with the North Star. (The difference between magnetic north and true north is called declination.) In the sixteenth and seventeenth centuries scientists began to better understand Earth’s magnetic fields.

American Elmer Sperry (1860–1930) built the first gyrocompass, a device that works day or night, anywhere on Earth—even at the poles, where lines of force are too close together for magnetic devices to function properly. When the gyrocompass is pointed north, it holds that position.

Before the compass, which simply indicates north by a means of a magnetic needle or needles that pivot, sailors used the sun, the moon, and the stars to determine direction and navigate their ships.