Magnetic North

The northerly reference direction indicated by a magnetic compass free from local compass error.

Magnetic north follows the local direction of the Earth’s magnetic field and differs from true north by magnetic variation, whose size and direction change with location and time. It should not be described simply as pointing directly at the moving north magnetic pole because the field is neither a perfect dipole nor geographically uniform.

A vessel’s own magnetism and nearby electrical or ferrous objects add deviation to the compass reading. Converting between true, magnetic and compass directions therefore requires the current charted variation and the vessel’s applicable deviation information.