How do magnetic compasses work?

A compass works by aligning its magnetic needle with the Earth's magnetic field, which is created by the iron core deep inside the planet. A compass is exactly accurate since the Earth's magnetic north differs slightly from Earth's true north.

Magnetic declination is the difference between magnetic north and true north, and modern navigators are able to calibrate their compasses to account for this difference, keeping them on track to reach their destinations. Compasses have been around for centuries and are easily made using a magnetized needle, water, and a cork or floating device that allows the needle to turn freely on the water.