Compass

The compass is a navigation instrument that uses Earth’s magnetic field to indicate direction. Its earliest known form appeared in China, where magnetized needles were used by at least the 11th century and probably earlier. Early Chinese magnetic devices were first associated with practices such as divination before the compass became an important aid to navigation. A simple magnetic compass contains a magnetized needle that can rotate freely.

Earth’s magnetic field causes the needle to align approximately along the north–south direction, allowing a user to identify magnetic north and other directions. Magnetic north is not exactly the same as geographic north, and the difference varies according to location and changes over time. A compass therefore provides direction rather than a complete position. The magnetic compass gradually spread beyond China and became an important tool for navigation across Asia, the Middle East, and Europe.

Its use at sea made it easier for sailors to maintain a general heading when landmarks were distant or the sky was cloudy. During the medieval and early modern periods, improvements in compass design made navigation more reliable and supported long-distance maritime travel. Compasses were also used for land navigation, surveying, and mapping. The instrument did not by itself make navigation precise: sailors and explorers also relied on charts, astronomical observations, landmarks, and knowledge of winds and currents.

Modern navigation systems such as satellite positioning have greatly increased accuracy, but magnetic compasses remain useful because they work without batteries or electronic signals. They are still carried on ships, aircraft, in outdoor equipment, and in emergency navigation kits.