Magnetic North – Direction the Magnetic Compass Points

What is Magnetic North?

Magnetic North is the direction indicated by the north-seeking end of a freely suspended magnetic needle, such as that found in a compass. Unlike True North, which points to the fixed Geographic North Pole at the top of Earth’s rotational axis (90°N latitude), Magnetic North is a moving point on the Earth’s surface where the geomagnetic field lines are vertical and directed downward.

This location is not static—it migrates due to complex, dynamic processes within Earth’s outer core. Currently (as of 2024), Magnetic North is situated in the Arctic Ocean, north of Canada, moving towards Siberia at a rate of about 40 kilometers per year, tracked by organizations like the National Centers for Environmental Information (NCEI) and the International Geomagnetic Reference Field (IGRF).

Magnetic North is vital for navigation in aviation, marine, and land contexts because magnetic compasses align with Earth’s horizontal magnetic field component. The location of Magnetic North is determined through direct measurement, satellite data, and geomagnetic models. It should not be confused with the Geomagnetic North Pole, which is a simplified theoretical construct.

Navigational charts, airport runway numbers, and heading references are traditionally based on Magnetic North, though modern GPS and satellite systems increasingly use True North. As Magnetic North moves, regular updates to navigational resources are essential for safety and accuracy.

True North (Geographic North)

True North, also known as Geographic North, is the direction along Earth’s surface that points directly to the Geographic North Pole—a fixed, physical point at 90°N where Earth’s axis of rotation meets its surface.

All longitude lines converge at this pole. Maps, charts, and global coordinate systems—including GPS—are referenced to True North. Unlike Magnetic North, True North does not change, making it the ultimate reference for precise positioning in aviation, surveying, and mapping.

However, because traditional compasses point to Magnetic North, navigators must account for the difference between the two—known as magnetic declination.

Magnetic Declination

Magnetic Declination (or variation) is the angle between True North and Magnetic North at a specific location. It is labeled east or west depending on whether Magnetic North lies east or west of True North from the observer’s perspective.

Declination varies by location and over time as Earth’s magnetic field evolves. For instance, in 2024, Maine (USA) has about 20° west declination, while Washington State is about 21° east. Navigators must account for declination to avoid significant errors.

National agencies like the NGDC chart and update declination values regularly. Aeronautical and nautical charts display current declination, and international standards require updates to this data for safe navigation.

The Earth’s Geodynamo: Source of the Magnetic Field

Earth’s magnetic field—and thus Magnetic North—originates from the outer core, composed of molten iron and nickel. The convective motion of this liquid metal generates electric currents, creating a powerful, changing geomagnetic field in a process called the geodynamo.

This field extends into space as the magnetosphere, shielding the planet from solar and cosmic radiation. The field is neither perfectly aligned with the rotation axis nor a simple dipole, producing regional anomalies and ongoing changes.

The movement of the core causes the Magnetic Poles to wander, tracked by satellites (such as ESA’s Swarm mission) and ground magnetometers. Understanding the geodynamo is key for geophysicists and anyone dependent on accurate compass readings.

Compasses and Magnetic Navigation

A magnetic compass is a simple, reliable device that has guided navigators for centuries. It uses a magnetized needle that aligns with the Earth’s magnetic field, with the north-seeking end pointing toward Magnetic North.

Handheld compasses, vehicle-mounted compasses, and more sophisticated gyrocompasses all rely on this principle. In aviation, compasses must be calibrated for local magnetic fields (deviation), acceleration, and turning effects.

The accuracy of compass navigation depends on understanding magnetic declination and local anomalies. Aviation runway numbers and headings, for example, are given in magnetic degrees and updated as the magnetic field shifts.

Magnetic North in Aviation

Aviation heavily relies on Magnetic North for headings, runway designations, and navigation aids. Runways are numbered according to their magnetic azimuth, rounded to the nearest ten degrees (e.g., Runway 27 for 270° magnetic).

As Magnetic North shifts, magnetic headings change, requiring airports to update runway numbers and charts. ICAO and FAA standards mandate frequent monitoring and updating of magnetic variation data.

Pilots must be aware of the difference between magnetic and true headings, especially when switching between compass-based and GPS navigation. Outdated magnetic data can lead to operational errors and safety risks.

Magnetic Variation and Aeronautical Charts

Magnetic Variation (declination) is shown on aeronautical, marine, and topographic charts using isogonic lines—lines connecting points of equal declination—and the agonic line, where declination is zero.

Aviation charts display current magnetic variation at key locations, updated at least every five years. This data enables pilots to convert between true and magnetic headings. Flight management systems and autopilots use magnetic variation tables to translate true courses into magnetic headings.

Notices to Airmen (NOTAMs) and Aeronautical Information Publications (AIPs) inform users of changes in magnetic variation and runway designations. Keeping this information up to date is crucial for flight safety.

Effects of Magnetic Dip and Compass Balance

Magnetic Dip is the angle at which Earth’s magnetic field lines intersect the surface. At the Magnetic Equator, the field is horizontal; near the Magnetic Poles, it is nearly vertical.

Compasses are balanced for specific regions. Using a compass outside its intended zone can cause the needle to drag or stick, especially in aviation and marine navigation. The IEC and ISO set standards for compass performance in different magnetic zones.

Pilots and mariners must ensure their compasses are suited for their operating area, or risk inaccurate readings due to magnetic dip.

Secular Variation and Magnetic Pole Drift

Secular Variation describes the gradual change in Earth’s magnetic field, primarily caused by the flow of molten metals in the outer core. This results in the slow drift of the Magnetic Poles and changes in local magnetic declination.

The Magnetic North Pole’s movement has accelerated in recent decades, moving from the Canadian Arctic towards Siberia at over 40 km per year. Scientists use ground, aerial, and satellite measurements to update global geomagnetic models, like the World Magnetic Model (WMM) and IGRF.

These updates ensure charts, navigation databases, and runway designations remain accurate and safe for use.

Polar Reversals and Paleomagnetism

Polar Reversals are events in which Earth’s magnetic field flips, exchanging Magnetic North and South. These reversals happen irregularly, with the last major event around 780,000 years ago.

Paleomagnetic studies of rocks record evidence of these reversals. While they are of scientific interest, reversals occur over thousands of years and do not affect short-term navigation. However, the ongoing drift of Magnetic North does, requiring regular system updates.

Adjustment for Magnetic Declination in Navigation

Navigators must adjust for magnetic declination to convert between compass (magnetic) and map (true) bearings.

• If declination is east, subtract it from the map bearing to get the compass bearing.
• If declination is west, add it to the map bearing.
• Reverse these steps when converting from compass to map bearings.

Declination Adjustment Table

Even a small adjustment error can lead to large positional errors over distance, making up-to-date declination essential for all navigators.

Practical Use Cases

Aviation: Pilots set heading indicators to local magnetic variation and update as they cross regions with different declinations. Runways are renumbered as magnetic headings shift.

Marine Navigation: Mariners steer with magnetic compasses and correct for local variation shown on nautical charts—especially important on long voyages.

Surveying: Surveyors switch between magnetic and true bearings to ensure property boundaries and land titles are accurate.

Land Navigation: Hikers and orienteers adjust for local declination to avoid errors in wilderness navigation.

Search and Rescue: Accurate bearings are crucial for coordinated searches and rescue operations.

Magnetic North and GPS Navigation

Most GPS receivers provide bearings relative to True North, using the WGS84 global reference system. Many devices can display magnetic north bearings by applying the latest geomagnetic models (e.g., the WMM).

This integration is vital for compatibility with traditional navigation systems. Users must check that their devices use up-to-date magnetic models and understand whether their readings are referenced to True or Magnetic North.

Common Misconceptions about Magnetic North

1. Compass Points to the North Pole:
   A compass points to Magnetic North, not the Geographic North Pole. The two can be separated by hundreds of kilometers.

2. Declination Is Constant:
   Declination changes over time. Maps and charts must be updated to remain accurate.

3. All Compasses Work Everywhere:
   Compasses are balanced for specific magnetic zones. Using them outside these regions can cause errors.

4. Declination Adjustment Is Optional:
   Ignoring it can result in large navigational errors, especially for professionals.

5. Magnetic North and True North Are Close Enough:
   In some places, the difference is over 20°, causing massive errors if ignored.

Magnetic North vs. True North: Comparison Table

Updating Navigation: The Importance of Current Data

Staying current with magnetic variation is essential. Aviation (ICAO, FAA, EASA) and maritime authorities (IHO, IMO) mandate updates to charts and databases to reflect new magnetic data. Always check the publication date of your charts and use official sources (such as NOAA’s online tools) for the most up-to-date declination values. Smartphone apps and navigation systems also require regular model updates.

Advanced Navigation: Integrating Magnetic and True Bearings

Professional navigation often involves converting between magnetic and true bearings. Aviation flight management systems, for example, calculate true courses from GPS or inertial sensors, then convert them to magnetic headings for cockpit displays using onboard magnetic models. Mastery of these conversions is critical for pilots and air traffic controllers, especially for international flights crossing regions with different magnetic characteristics.

Magnetic North is a dynamic, essential concept for anyone navigating by compass, from pilots and mariners to surveyors and hikers. Understanding its behavior, how to adjust for it, and the need for up-to-date data ensures safe, accurate, and efficient navigation worldwide.