True north
True north is the direction along Earth's surface towards the geographic North Pole or True North Pole.
Geodetic north differs from magnetic north, and from grid north. Geodetic true north also differs very slightly from astronomical true north because the local gravity may not point at the exact rotational axis of Earth.
The direction of astronomical true north is marked in the skies by the north celestial pole. This is within about 1° of the position of Polaris, so that the star would appear to trace a tiny circle in the sky each sidereal day. Due to the axial precession of Earth, true north rotates in an arc with respect to the stars that takes approximately 25,000 years to complete. Around 2101–2103, Polaris will make its closest approach to the celestial north pole. The visible star nearest the north celestial pole 5,000 years ago was Thuban.
On maps published by the United States Geological Survey and the United States Armed Forces, true north is marked with a line terminating in a five-pointed star. The east and west edges of the USGS topographic quadrangle maps of the United States are meridians of longitude, thus indicating true north. Maps issued by the United Kingdom Ordnance Survey contain a diagram showing the difference between true north, grid north, and magnetic north at a point on the sheet; the edges of the map are likely to follow grid directions rather than true, and the map will thus be truly rectangular/square.
