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Somewhat more formally, Bowditch defines variation as "the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north. The angle between magnetic and grid meridians is called grid magnetic angle, grid variation, or grivation." [1] By ...
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 bodies ...
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]
8 - Magnetic heading, the compass heading corrected for magnetic deviation but not magnetic variation; thus, the heading reliative to magnetic north. 9, 10 - Effects of crosswind and tidal current, causing the vessel's track to differ from its heading. A, B - Vessel's track. TVMDC,AW is a mnemonic for converting from true heading, to magnetic ...
In surveying, bearings can be referenced to true north, magnetic north, grid north (the Y axis of a map projection), or a previous map, which is often a historical magnetic north. [citation needed] If navigating by gyrocompass, the reference direction is true north, in which case the terms true bearing and geodetic bearing are used.
The magnetic pole moved along the northern Canadian shore for centuries, Dr Brown said. It drifted into the Arctic Ocean in the 1990s, and after that, it accelerated and headed towards Siberia.
3 – Magnetic north, which differs from true north by the magnetic variation. 4 – Compass north, including a two-part error; the magnetic variation (6) and the ship's own magnetic field (5) 5 – Magnetic deviation, caused by vessel's magnetic field. 6 – Magnetic variation, caused by variations in Earth's magnetic field.
Compass needles in the Northern Hemisphere point toward the magnetic North Pole, although the exact location of it changes from time to time as the contours of Earth’s magnetic field also change.