bearing

A bearing is the direction of a fixed point, or the path of a moving object, from a point of observation on the Earth's surface, expressed as an angle from the north. In the diagram, the bearing of a point A from an observer at B is the angle between the line BA and the north line through B, measured in a clockwise direction from the north line.

Direction of a fixed point, or the path of a moving object, from a point of observation. Bearings are angles measured in degrees (°) from the north line in a clockwise direction. A bearing must always have three figures. For instance, north is 000°, northeast is 045°, south is 180°, and southwest is 225°.

True north differs slightly from magnetic north (the direction in which a compass needle points), hence northeast may be denoted as 045M or 045T, depending on whether the reference line is magnetic (M) or true (T) north. True north also differs slightly from grid north since it is impossible to show a sphere on a flat map.

Finding a bearing To find the bearing of B from A, start at A facing north then turn clockwise until facing B. The bearing of B from A is the angle shaded:

To find the bearing of A from B, start at B facing north, then turn clockwise until facing A. The bearing of A from B is the angle shaded:

Problem solving Trigonometry, Pythagoras' theorem, and scale drawings are often used when solving problems involving bearings.

For example, if a ship sails from harbour to an island 10 km away on a bearing of 030°, then continues on from the island at a bearing of 180° to a point that is on a bearing of 090° from the harbour, it is possible to measure how far the ship is from the harbour using trigonometry.

sin 30° = opp/hyp = distance from harbour/10 10 × sin 30° = distance from harbour = 5 km