True north is the direction along the earth's surface towards the geographic
North Pole.
True north usually differs from
magnetic north (the direction of the
magnetic north pole) and
grid north (the direction northwards along the grid lines of a
map projection).
The direction of true north is marked in the skies by the
north celestial pole. For most practical purposes, this is the position of
Polaris. However, due to the
precession of the Earth's
axis, true north rotates in an arc that takes approximately 25,000 years to complete. In 2102 Polaris will make its closest approach to the celestial north pole. 5,000 years ago, the closest star to the celestial north pole was
Thuban.
On maps issued by the
United States Geological Survey, and the
U.S. military, true north is marked with a line terminating in a five-pointed star. 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.