Earth's Shield Right Now
Earth's magnetic field wraps the planet in an invisible shield. A stream of particles from the Sun, the solar wind, pushes on it all the time. The picture below is drawn from live readings: the faster and denser the solar wind, the closer the edge of the shield is pushed toward Earth, and the stronger the storm, the brighter the ring of current around Earth and the farther the aurora spreads. Click or tap the picture to see it full screen.
Not to scale: Earth is drawn larger so its features show. Distances out to the shield edge and the bow shock follow the live readings. The bow shock is where the solar wind, which normally flows faster than sound travels in space, suddenly slows down and piles up as it meets Earth’s magnetic field, much like the wave that forms in front of a moving boat’s bow. On the side facing the Sun it usually sits about 20,000 km (12,000 mi) farther out than the shield edge.
The Long View
The slow changes deep inside Earth: the field's overall strength, the wandering magnetic poles, and the growing weak spot over the South Atlantic. These come from the International Geomagnetic Reference Field (IGRF), the world's standard model of the field, built from observatories and satellites and renewed every five years. Values after 2025 are the model's forecast.
Solar Storms & The Magnetic Field
When the Sun throws off a burst of fast solar wind or a cloud of charged gas (a coronal mass ejection), it slams into Earth's magnetic field. If the cloud's own magnetism points south, it links up with Earth's field and pours energy in. The result is a geomagnetic storm: the shield is squeezed, electric currents surge around the planet, auroras spread toward the equator, and power grids, satellites and GPS can be disrupted. The live readings above track exactly this.
The Weakening Field
Earth's magnetic field is made by molten iron churning in the outer core, about 1,800 miles (2,900 km) beneath our feet. Since careful measurements began in the 1830s, the field's overall strength has dropped by about 9 percent, and the weakening is not even: some regions are fading much faster than others. Scientists debate what it means. Some see a normal swing that will recover; others see the early stages of an excursion or reversal.
Magnetic Pole Drift
The magnetic north pole, where a compass needle points straight down, is not fixed. For most of the 1900s it crept slowly across northern Canada. In the 1990s it sped up, reaching about 35 miles (55 km) a year around 2000, and raced across the Arctic Ocean toward Siberia; it has slowed since, to about 22 miles (35 km) a year. The magnetic south pole has drifted off the coast of Antarctica. Maps, phones, airports and militaries all depend on tracking these moves.
The South Atlantic Anomaly (SAA)
A large region over South America and the South Atlantic where the magnetic field is far weaker than anywhere else at the same latitudes. Radiation reaches closer to Earth here, so satellites and the space station take extra hits as they pass over. The weak spot has been growing, drifting west and splitting into two low points.
Jerks, Excursions & Reversals
Every few years the field's steady drift changes direction abruptly; these "geomagnetic jerks" show up at observatories around the world. Over longer spans, the field sometimes collapses and briefly flips before recovering (an excursion, like the Laschamp event about 41,000 years ago), or flips for good (a reversal; the last one was about 780,000 years ago). Researchers study rocks, lava, sediments and ice to learn how fast these changes happen and what they did to life on Earth.