They have two main advantages over magnetic compasses: It is a non-magnetic compass that finds true north by using an (electrically powered) fast-spinning wheel and friction forces in order to exploit the rotation of the Earth. the gyrocompass and GPS-compass.Ī gyrocompass is similar to a gyroscope. Two sensors that utilize two of the remaining six principles are often also called compasses, i.e. There are other ways to find north than the use of magnetism, and from a navigational point of view a total of seven possible ways exist (where magnetism is one of the seven).
Some magnetic compasses include means to manually compensate for the magnetic declination, so that the compass shows true directions. The effect of this means a map with the latest declination information should be used. The locations of the Earth's magnetic poles slowly change with time, which is referred to as geomagnetic secular variation. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north.
Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north, called magnetic declination can vary widely with geographic location. In navigation, directions on maps are usually expressed with reference to geographical or true north, the direction toward the Geographical North Pole, the rotation axis of the Earth. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation. The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily. The magnetic field exerts a torque on the needle, pulling the North end or pole of the needle approximately toward the Earth's North magnetic pole, and pulling the other toward the Earth's South magnetic pole. It functions as a pointer to " magnetic north", the local magnetic meridian, because the magnetized needle at its heart aligns itself with the horizontal component of the Earth's magnetic field. The magnetic compass is the most familiar compass type. Ī military compass that was used during World War I
The first usage of a compass recorded in Western Europe and the Islamic world occurred around 1190. 206 BC), and later adopted for navigation by the Song Dynasty Chinese during the 11th century. If local variation between magnetic north and true north is known, then direction of magnetic north also gives direction of true north.Īmong the Four Great Inventions, the magnetic compass was first invented as a device for divination as early as the Chinese Han Dynasty (since c. These numbers allow the compass to show azimuths or bearings which are commonly stated in degrees. Other methods may be used, including gyroscopes, magnetometers, and GPS receivers.Ĭompasses often show angles in degrees: north corresponds to 0°, and the angles increase clockwise, so east is 90°, south is 180°, and west is 270°. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with magnetic north. Most smartphones contain a magnetometer that can function as a compass.Ī compass is a device that shows the cardinal directions used for navigation and geographic orientation.
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