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Magnetic declination (also called magnetic variation) is the angle between magnetic north and true north at a particular location on the Earth's surface. The angle can change over time due to polar wandering .
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 ...
The International Geomagnetic Reference Field (IGRF) is a standard mathematical description of the large-scale structure of the Earth's main magnetic field and its secular variation. It was created by fitting parameters of a mathematical model of the magnetic field to measured magnetic field data from surveys, observatories and satellites ...
Changes in Earth's magnetic field on a time scale of a year or more are referred to as secular variation. Over hundreds of years, magnetic declination is observed to vary over tens of degrees. [13] The animation shows how global declinations have changed over the last few centuries. [34] The direction and intensity of the dipole change over time.
The Enhanced Magnetic Model (EMM) is a sister product of the NGDC featuring a much higher amount of data to degree and order 790, giving a wavelength of 51 km as opposed to the 3000 km of WMM. At this resolution, it is not only able to model the Earth's magnetic field at the core-mantle boundary ("main field"), but also take into account ...
By setting the date and latitude, the true north and the magnetic variation could be read from the instrument without the need for calculation. [8] With the iron vessels introduced in the 19th century the azimuth compass would be mounted on a pedestal at a neutral point where the readings would not be affected by magnetism of the vessel.
Secular variation can be observed in measurements at magnetic observatories, some of which have been operating for hundreds of years (the Kew Observatory, for example). Over such a time scale, magnetic declination is observed to vary over tens of degrees. [1] A movie on the right shows how global declinations have changed over the last few ...
A magnetic compass's user can determine true North by finding the magnetic north and then correcting for variation and deviation. Variation is defined as the angle between the direction of true (geographic) north and the direction of the meridian between the magnetic poles.