Bearing (navigation): definitions, types, methods, and common uses

Common references and notation

Bearing measurements are normally expressed in degrees, typically measured clockwise from a reference. The most common references are Cardinal directions as found with a cardinal system and a compass. When celestial objects are used as references, stars and the sun are typical choices: observers take bearings of bright stars or the sun to establish position. On land, fixed features such as mountains or man-made beacons provide reliable references; at sea, lighthouses and buoys serve the same role.

Types of bearings

• True bearing: angle measured from geographic (true) north.
• Magnetic bearing: angle measured from magnetic north as indicated by a magnetic compass.
• Compass bearing: the bearing read directly from a magnetic compass, which may include compass errors.
• Relative bearing: angle measured clockwise from the vessel's or aircraft's heading to a target.

Methods and instruments

Bearings can be obtained optically, electronically, or by radio. Optical methods use sights, binoculars with reticles, or a sextant to take an angle to a visible object. Radar provides electronic bearings to reflected targets and is widely used at sea and in poor visibility; a basic radar example is discussed at radar. Radio direction-finding systems (ADF) and modern GNSS-derived azimuths also supply bearing information. Common instruments include the magnetic compass, pelorus (a bearing indicator), gyrocompass, and radar or radio receivers.

History and development

The practice of taking bearings dates back to ancient navigation when sailors used the sun and stars for direction. The magnetic compass, introduced to widespread maritime use centuries ago, allowed bearings relative to magnetic north. Over time mechanical and electronic devices improved accuracy: gyrocompasses reduced magnetic error, radar and radio bearings enabled night and low-visibility navigation, and satellite systems now supply precise positions and courses.

Uses, examples, and important distinctions

Bearing information is applied to plot lines of position, fix a vessel's or vehicle's location, steer a course, and avoid collisions. For example, taking bearings to two known landmarks gives a position fix at their intersection. It is important to distinguish bearing from related terms: bearing is a direction to an object, while heading is the direction the craft points, and course is the intended path over the ground. Bearings must be corrected for magnetic variation and compass deviation when converting between true and magnetic frames; simple rules of thumb and published variation charts are used for those conversions.

Limitations and errors

Sources of error include instrument inaccuracies, human reading mistakes, magnetic interference, and environmental effects such as refraction. Radar bearings are affected by antenna alignment and target characteristics, and radio bearings depend on signal propagation. Good practice involves taking multiple bearings, using different references, and applying known corrections to reduce uncertainty.

Further reading and resources: general discussions of bearings and related navigation topics can be found via introductory pages on navigation fundamentals and specific instrument guides available from navigation authorities and manuals (compass guides, radar manuals, and maritime mark catalogues such as lists of lighthouses and buoys). Practical shore and celestial methods trace back to traditional use of stars and the sun, while modern electronic systems complement optical bearings and fixed-land references like mountains and beacons.

For concise definitions and examples of common bearing problems and solutions, introductory navigation textbooks and pilotage handbooks remain useful starting points; specialized procedures for aircraft, marine, and land navigation detail equipment-specific techniques and error corrections, and radio/ radar procedures are set out in operational guides and standards (overview, angles and geometry).