compass

A compass is a device used for navigation and orientation that indicates direction relative to the Earth's magnetic field or, in some designs, to true north. The most familiar form is the magnetic compass, which uses a magnetized needle balanced on a low-friction pivot inside a protective housing. The needle freely aligns with the horizontal component of the Earth’s magnetic field and typically points toward magnetic north. Many compasses include a scale or card marked with directions and a mechanism to adjust for magnetic declination so magnetic bearings can be converted to true bearings.

Principle and operation

The compass relies on magnetism. A freely rotating magnetized needle aligns with the Earth’s magnetic field, which varies by location and over time. The result is a stable reference direction that navigators use to determine azimuths or bearings. Because magnetic north does not coincide exactly with geographic north, users often apply a local magnetic declination to translate magnetic directions into true directions.

History

The compass originated in ancient China, where lodestones were used for geomancy and early navigational purposes. By the Song dynasty (around the 11th century) a magnetized needle on a pivot was used for maritime guidance, and knowledge spread to Europe by the 12th century. Over centuries, improvements included better suspension, damping, and standardized graduations on a compass card, enabling more reliable navigation at sea.

Types and technologies

Besides the classic magnetic compass, other varieties include the gyrocompass (which points to true north using a gyroscope), and electronic or digital compasses that rely on magnetometers in smartphones and other devices. More advanced instruments may incorporate fluxgate sensors or Hall-effect devices to determine heading.

Limitations

Compass readings can be affected by local magnetic anomalies, nearby ferromagnetic materials, or electrical equipment. Magnetic declination varies by location and time, so corrections are necessary for accurate navigation. Near the magnetic poles, a compass becomes unreliable.

Uses

Compasses are used in marine and air navigation, land surveying, hiking, orienteering, and in many modern devices as part of a broader navigation system.