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Earth's magnetic field
Beginner
Earth acts as a giant bar magnet.
Earth's field is roughly a dipole of 25–65 μT from circulating liquid iron in the outer core (the geodynamo). It deflects solar wind and guides compasses.
The field has reversed many times over geological history.
The magnetic poles drift and are offset from the geographic poles.
In more detail
Earth behaves like a large magnet, with a field produced by motion in its liquid outer core. The field deflects charged particles from the Sun and shields the surface.
Real-world uses
- Navigators use compasses that align with Earth's field.
- Geologists study magnetic rocks to reconstruct past field reversals.
- Compasses, sailors and migrating birds all use the Earth's magnetic field to find their direction.
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Frequently asked questions
Why does the compass point north?
The needle aligns with Earth's magnetic field, whose south pole is near the geographic north.
Is the field strength constant?
No, it varies over time and location, and it reverses periodically.
Why does a compass point north?
The compass needle is a magnet that aligns with the Earth's field, whose field lines run roughly from the south to the north geographic pole.
Related topics in Magnetism & Induction
Magnets and poles · Magnetic field lines · Magnetic force on a moving charge · Circular motion in B field · Cyclotron frequency