1The Earth is a magnet
The Earth has a magnetic field shaped like a giant bar magnet's. Its magnetic poles are close to, but not exactly at, the geographic North and South Poles.
magnetic field
Lesson 27.3 notes
Earth's magnetism
The Earth as a giant magnet, compasses, bearings and finding your way.
2Where it comes from
The field is made by liquid iron flowing in the Earth's outer core as the planet spins. It can't be a buried bar magnet: the core is far too hot.
outer core
3Why a compass points north
A compass needle is a magnet. Its north end is pulled towards the magnetic pole near the North Pole, so that pole must really be a magnetic south pole.
4Turning a compass
Turn a compass round and the needle keeps pointing north: the Earth's field holds it. To take a bearing, turn the dial until its N lines up with the needle.
5Bearings
Directions are given as bearings: angles measured clockwise from north. North is 000°, east 090°, south 180° and west 270°.
bearing
6Finding your way
A compass works without batteries or a signal, so walkers, sailors and pilots still use one for navigation. Follow a bearing and you keep going the same way, even in fog.
navigation
7A shield in space
Out in space, the Earth's field steers away harmful particles streaming from the Sun. Near the poles some get through and make the glowing aurora.
aurora
Explore: Compass lab
Drag the compass round the Earth and watch the needle. Then follow bearings across a misty hill to reach the hut.
Common mistake: A compass points to a magnetic south pole
Unlike poles attract. The end of a compass needle that points north is its north pole, so the magnetic pole near the geographic North Pole is really a magnetic south pole.
Remember
- The Earth has a magnetic field like a giant bar magnet's, made by liquid iron moving in its outer core.
- A compass needle is a magnet: its north end points to magnetic north, near the geographic North Pole.
- Bearings are measured clockwise from north: east is 090°, south 180° and west 270°.
Going further at GCSE