The Earth has two north poles. One of them is true north, the point at one end of the Earth's axis. A compass needle is a small magnet balanced on a pin so that it is free to point in any direction. Since magnets are attracted to each other, the compass needle lines itself up with the magnetic north. No one knows exactly how the Earth generates its magnetism, but it is believed to come from the molten iron in the Earth's core.
All magnets have fields, or areas where their pull can be felt.
The Earth's magnetic field is so large that we are always in it, which is why a compass always points north. Many metals, such as iron, that remain in a magnetic field for a long time will become magnets themselves, so many magnets can be found naturally. It was the discovery of a magnetic rock, first known as lodestone , in the 1100s that enabled ships to sail out of sight of land and still know where they were. The lodestone always pointed north.