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Magnetic declination. Angle on the horizontal plane between magnetic north and true north. Example of magnetic declination showing a compass needle with a "positive" (or "easterly") variation from geographic north. N g is geographic or true north, N m is magnetic north, and δ is magnetic declination. Magnetic declination (also called magnetic ...
The local angular difference between magnetic north and true north is called the magnetic declination. Most map coordinate systems are based on true north, and magnetic declination is often shown on map legends so that the direction of true north can be determined from north as indicated by a compass. [28]
Earth's magnetic field, predominantly dipolar at its surface, is distorted further out by the solar wind. This is a stream of charged particles leaving the Sun's corona and accelerating to a speed of 200 to 1000 kilometres per second. They carry with them a magnetic field, the interplanetary magnetic field (IMF).
The earliest reference to a specific magnetic "direction finder" device for land navigation is recorded in a Song dynasty book dated to 1040–44. There is a description of an iron "south-pointing fish" floating in a bowl of water, aligning itself to the south.
The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. The locations of the Earth's magnetic poles slowly change with time, which is referred to as geomagnetic secular variation. The effect of this means a map with the latest declination information should be used. [9]
World Magnetic Model. Magnetic declination map at sea-level for the year 2010 derived from WMM2010. The World Magnetic Model (WMM) is a large spatial-scale representation of the Earth's magnetic field. It was developed jointly by the US National Geophysical Data Center and the British Geological Survey. The data and updates are issued by the US ...
In navigation, the heading of a vessel or aircraft is the compass direction in which the craft's bow or nose is pointed. Note that the heading may not necessarily be the direction that the vehicle actually travels, which is known as its course. [a] Any difference between the heading and course is due to the motion of the underlying medium, the ...
The first is magnetic declination or variation—the angular difference between magnetic North (the local direction of the Earth's magnetic field) and true North. [1] The second is magnetic deviation —the angular difference between magnetic North and the compass needle due to nearby sources of interference such as magnetically permeable ...