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True North is the direction toward the geographic point on the Northern hemisphere where the Earth's axis of rotation intersects with the Earth's surface. This position is also called the Earth's geographic North pole. The Earth's rotational axis is the same as the celestial axis and the North axis points almost at Polaris, the North Star.

Compasses align themselves along the Earth's magnetic axis. The Earth's North magnetic pole is the point on the Northern Hemisphere where the Earth's magnetic axis intersects with the Earth's surface. The magnetic North pole is not in the same geographic position as the geographic North pole. There are also variations in the Earth's magnetic lines of force that cause compasses to point along these lines of force and not toward the magnetic North pole. The geographic position of the Earth's North magnetic pole also changes over time as do the curvatures of the magnetic lines of force. For these reasons, all professional surveying and geodetic marks are established with reference to true North, not magnetic North.

true North (last edited 2009-03-21 21:03:18 by localhost)