Earth’s magnetic field — Earth science, 14–17 years
How moving metal deep inside Earth creates a shield and a compass direction. Earth science, 14–17 years.
An invisible shield
Earth acts like a giant magnet, with a magnetic field extending far into space. It is produced mainly by moving, electrically conducting liquid metal in the outer core. The field gives compass needles a direction and deflects much of the charged particle flow from the Sun.
The problem it helps solve
A compass can point north even when there is no landmark nearby, but early explanations had to account for this invisible force. The magnetic field also helps explain why Earth is not exposed directly to all solar particles. It is not a solid wall: some particles enter near the poles and can produce auroras.
Reading a compass
Place a compass flat and wait for its needle to stop. The marked end points towards magnetic north, not exactly the geographic North Pole. If it points at 8° on a map scale while the route should be 20° east, turn 12° clockwise. Local rocks and nearby metal can disturb the reading, so check more than once.
Magnetic north is not geographic north
It is reasonable to think that the end labelled north on a compass points exactly to the North Pole. It actually follows the local magnetic field, whose direction changes with place and slowly changes over time. Maps and navigation systems correct for this difference, called magnetic declination.
Where it appears outside school
Magnetic fields are used in compasses, aircraft navigation, satellites and some surveys of rocks beneath the ground. Space agencies monitor the field because strong solar storms can disturb radio communication, satellites and electrical networks. Researchers also study ancient magnetism locked in rocks to learn how the field changed in the past.
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