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Original file (5,400 × 4,500 pixels, file size: 3.06 MB, MIME type: application/pdf) This is a file from the Wikimedia Commons . Information from its description page there is shown below.
Size of this JPG preview of this PDF file: 800 × 533 pixels. ... Map of magnetic declination in 2015. Date: 14 December 2014: ... Version of PDF format: 1.5
English: This is a world map of magnetic declination created by the National Geophysical Data Center at NOAA. Français : Carte mondiale de la déclinaison magnétique terrestre créé par le centre national des donnée géophysiques ( NGDC ) de l'agence américaine responsable de l'étude de l'océan et de l'atmosphère ( NOAA ).
N g is geographic or true north, N m is magnetic north, and δ is magnetic declination. 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.
Magnetic declination. A compass needle does not in general point true north. The variation from true north varies with location, and it was suggested that this could provide a basis for determination of longitude. With the exception of magnetic declination, all proved practicable methods. Developments on land and sea, however, were very different.
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 .
18th-century azimuthal compass held in the National Archaeological Museum of Spain. An azimuth compass (or azimuthal compass) is a nautical instrument used to measure the magnetic azimuth, the angle of the arc on the horizon between the direction of the Sun or some other celestial object and the magnetic north.