Earth’s magnetic field — Earth science, 11–13 years
Earth acts like a giant magnet, making a shield that guides compasses and helps protect life from particles from the Sun.
What the field is
Deep inside Earth, moving liquid metal makes an invisible magnetic field around the planet. It has a north and a south magnetic pole, so a compass needle turns to line up with it. The field also deflects many charged particles arriving from the Sun.
Why it matters
Long ago, people needed a direction finder when roads, landmarks and clouds gave no reliable clue. A magnetised needle solved that problem because it responds to Earth’s field. The same invisible shield matters today: without it, more solar particles could reach the atmosphere and damage satellites or disrupt radio signals.
A compass test
Place a compass flat on a table, away from speakers, phones and metal objects. Wait until the needle stops moving, then turn the compass case so its north mark matches the needle’s north end. Walk ten metres and repeat: the needle points nearly the same way because the field reaches both places.
The common mix-up
It is easy to say that a compass points exactly to geographic north, because its end is labelled N and maps put north at the top. In fact, it follows magnetic north, which is not in precisely the same place and slowly shifts. Nearby iron or an electric device can also pull the needle away from the correct direction.
Where it appears
Compasses help hikers, sailors and aircraft systems keep track of direction, although modern navigation also uses satellites and maps. Near the polar regions, solar particles guided by the field can make auroras: curtains of green, red or purple light. Scientists study these lights to learn about space weather.
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