Scientific model · World Magnetic Model 2025 (NOAA and the British Geological Survey): a scientific model fitted to satellite and observatory measurements, valid to 2029
Earth's magnetic field
The Earth behaves like a giant, slightly tilted magnet. The short needles show the direction of its magnetic field at the surface, coloured by strength, and the card shows what a compass does where you are.
Where the field comes from
About 2,900 km below your feet, the Earth's outer core is liquid iron and nickel. As it churns, driven by heat escaping from the inner core and steered by the Earth's spin, it generates electric currents, and those currents create the magnetic field. This is called the geodynamo.
Why your compass is not quite right
A compass points to magnetic north, not to the geographic North Pole. The difference, called declination, depends on where you are and changes slowly over the years. Pilots, sailors and phone compasses all correct for it using models like the one in this app.
The wandering pole
The north magnetic pole moves. In 1900 it was in northern Canada; since then it has moved about 2,500 km towards Siberia, at up to about 55 km a year. Its positions are calculated from models fitted to observations; before 1900 those models rely on historical compass records.
A shield against the Sun
The field deflects most of the charged particles streaming from the Sun. During a geomagnetic storm (Kp 5 or more), some of those particles are guided down near the magnetic poles and make the air glow: the aurora. Over the South Atlantic the field is unusually weak, so satellites passing through the 'South Atlantic Anomaly' meet more radiation.
Did you know?
The Earth's magnetic field has flipped many times: the last full reversal, when a compass would have pointed south, happened about 780,000 years ago. The record of these flips is frozen into the rocks of the ocean floor on either side of the spreading ridges.