How Does a Compass Work?

CREDIT: Timwege | Dreamstime

If you're lost in the woods, your best chance of finding your way might be a tiny magnet.

A magnet is what makes a compass point north -- the small magnetic pin in a compass is suspended so that it can spin freely inside its casing and respond to our planet's magnetism.

A compass needle aligns itself and points toward the top of Earth's magnetic field, giving explorers and lost souls a consistent sense of direction.

How it works

A compass points north because all magnets have two poles , a north pole and a south pole, and the north pole of one magnet is attracted to the south pole of another magnet. (You may have seen this demonstrated by a pair of simple bar magnets or refrigerator magnets pushed end to end.)

The Earth is a magnet that can interact with other magnets in this way, so the north end of a compass magnet is drawn to align with the Earth's magnetic field. Because the Earth's magnetic North Pole attracts the "north" ends of other magnets, it is technically the "South Pole" of our planet's magnetic field.

True north

While a compass is a great tool for navigation, it doesn't always point exactly north. This is because the Earth's magnetic North Pole is not the same as "true north," or the Earth's geographic North Pole . The magnetic North Pole lies about 1,000 miles south of true north, in Canada.

And making things even more difficult for the compass-wielding navigator, the magnetic North Pole isn't even a stationary point. As the Earth's magnetic field changes, the magnetic North Pole moves. Over the last century, it has shifted more than 620 miles (1,000 kilometers) toward Siberia, according to scientists at Oregon State University.

This difference between true north and the north heading on a compass is an angle called declination. Declination varies from place to place because the Earth's magnetic field is not uniform it dips and undulates.

These local disturbances in the field can cause a compass needle to point away from both the geographic North Pole and the magnetic North Pole. According to the United States Geological Survey, at very high latitudes , a compass needle can even point south.

By using charts of declination or local calibrations, compass users can compensate for these differences and point themselves in the right direction.

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