A device that uses the Earth's magnetic field to indicate which way north is a compass.

Here's how it works:

* Magnetic Needle: A compass contains a small, freely rotating magnetic needle.

* Earth's Magnetic Field: The Earth acts like a giant magnet, generating a magnetic field that extends from its core to space.

* Alignment: The magnetic needle in the compass aligns itself with the Earth's magnetic field lines, pointing towards magnetic north.

* North Pole: Magnetic north is not exactly the same as the geographic North Pole, but it's close enough for practical navigation.

Let me know if you have more questions about compasses or Earth's magnetic field!