Earth’s surface has two distinct “North” points that are separated by a significant distance, which poses a continuous challenge for navigation. True North and Magnetic North are two entirely different concepts, though both relate to a northward direction. The former is a fixed geographic location, while the latter is a constantly shifting point related to the planet’s magnetic field. Understanding the difference between these two poles, why one moves and the other does not, and how to account for the disparity is fundamental for anyone who relies on a map and compass to find their way.
True North: The Geographic Anchor
True North, also known as the Geographic North Pole, is the fixed point where the Earth’s axis of rotation intersects the surface of the planet. This location remains stationary for all practical purposes. Because it is tied to the physical spin of the Earth, the Geographic North Pole is the reference point for all map projections and the global coordinate system of latitude and longitude. Every line of longitude, or meridian, begins at the Geographic North Pole. Navigators and surveyors use this pole as the single, unchanging reference for orientation and mapping.
Magnetic North: The Wandering Pole
Magnetic North is the location on the Earth’s surface where the planet’s magnetic field lines converge and point vertically downward. This is the point toward which the north-seeking end of a magnetic compass needle is drawn. Unlike its geographic counterpart, the Magnetic North Pole is not fixed and is perpetually in motion.
This wandering is driven by changes in the Earth’s core, causing the magnetic field to fluctuate daily and yearly. Since its discovery in the 1830s, the Magnetic North Pole has traveled over 1,400 miles, moving from northern Canada toward Siberia. The pole’s movement has accelerated significantly in recent decades, sometimes shifting at a rate of up to 31 miles per year.
Measuring the Difference: Magnetic Declination
The difference between True North and Magnetic North is quantified by a measurement called magnetic declination, or magnetic variation. Declination is the angle, measured in degrees, between the direction of True North and the direction the compass needle points at any specific location on Earth. This angle is not uniform globally; it changes depending on a person’s position on the planet and evolves over time as the Magnetic North Pole shifts.
Magnetic declination is considered positive when Magnetic North is east of True North and negative when it is west. For navigation, this value is necessary to convert a compass reading, which points to Magnetic North, into a true bearing aligned with the fixed Geographic North. Navigators, pilots, and surveyors use specialized charts to determine the exact declination for their area.
These charts feature isogonic lines, which are lines connecting all points on the Earth’s surface that share the same magnetic declination value. An agonic line is a special isogonic line where the declination is zero, meaning True North and Magnetic North are perfectly aligned at that location. Because the magnetic field is always changing, these declination values and their associated isogonic lines must be regularly updated, often every five years, to maintain the accuracy of modern navigation systems and charts.
The Geophysics Behind the Poles
The Earth’s magnetic field, which creates the Magnetic North Pole, is generated deep within the planet by a process known as the geodynamo effect. This mechanism is powered by the movement of molten metal in the Earth’s outer core, a layer composed primarily of liquid iron and nickel. Heat escaping from the core drives convection currents within this electrically conductive fluid.
The combination of these convection currents and the Earth’s rotation creates a self-sustaining electromagnetic field. As the molten iron flows, it generates electric currents which, in turn, produce the magnetic field that extends far into space. Because the fluid dynamics of the outer core are in constant flux, the resulting magnetic field is not perfectly aligned with the Earth’s rotational axis. This misalignment is the fundamental reason why the Magnetic North Pole is separate from the Geographic North Pole and why it is always moving.