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The true meridian is the chord that goes from one pole to the other, passing through the observer, and is contrasted with the magnetic meridian, which goes through the magnetic poles and the observer. The true meridian can be found by careful astronomical observations, and the magnetic meridian is simply parallel to the compass needle.
A magnetic compass points to magnetic north, not geographic (true) north. Compasses of the style commonly used for hiking (i.e., baseplate or protractor compass) utilize a dial or bezel which rotates 360 degrees and is independent of the magnetic needle. To manually establish a declination for true north, the bezel is rotated until the desired ...
The meridian on the celestial sphere. An observer's upper meridian, a semicircle contains their zenith and both celestial poles; the observer's local meridian is the semicircle that passes through their zenith and the north and south points of their horizon.
The WGS 84 meridian of zero longitude is the IERS Reference Meridian, [8] 5.3 arc seconds or 102 metres (335 ft) east of the Greenwich meridian at the latitude of the Royal Observatory. [ 9 ] [ 10 ] (This is related to the fact that the local gravity field at Greenwich does not point exactly through the Earth's center of mass, but rather ...
Mercator suggested that the magnetic north pole was an island in the longitude of the Azores, where magnetic declination was, at that time, close to zero. These ideas were supported by Michiel Coignet in his Nautical Instruction. [55] Halley made extensive studies of magnetic variation during his voyages on the pink Paramour.
A magnetic field is a vector field, but if it is expressed in Cartesian components X, Y, Z, each component is the derivative of the same scalar function called the magnetic potential. Analyses of the Earth's magnetic field use a modified version of the usual spherical harmonics that differ by a multiplicative factor.
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The north magnetic pole, also known as the magnetic north pole, is a point on the surface of Earth's Northern Hemisphere at which the planet's magnetic field points vertically downward (in other words, if a magnetic compass needle is allowed to rotate in three dimensions, it will point straight down).