A magnetic field is the three-dimensional area around a magnet in which the magnet exerts force on other objects. The invisible magnetic field of a simple bar magnet can be visualized by placing iron filings around it (SF Fig. 7.5). The magnet exerts force on the iron filings causing them to move and align with the magnet’s magnetic field lines. Every magnet has a north pole (often colored red and labeled “N”) and a south pole (often colored blue and labeled “S”). Opposite magnetic poles are attracted to each other. For example, the north pole of one magnet would be attracted to the south pole of a second magnet.

Earth has a strong magnetic field (SF Fig. 7.6) with magnetic poles. Earth’s magnetic field originates it its core, which is primarily made of the magnetic material iron. Earth’s magnetic field is generated and maintained by the fluid outer core moving around the solid inner core to induce electric currents. These electric currents generate magnetic fields perpendicular to the flow of electric charge. This process is described by the dynamo theory and it applies to many other celestial bodies.

Wayfinders have long been able to navigate from place to place with the use of simple magnetic compasses. Compass needles orient themselves towards the magnetic poles of Earth. The so-called “North Pole” in the Arctic Circle is actually the south pole of Earth’s magnetic field. It is called the North Pole because the north pole of compass needles point toward it. Similarly, the south pole of a magnetic compass needle is attracted to the north pole of Earth’s magnetic field found off the coast of Antarctica. The earth’s magnetic poles are not the same as the earth’s geographical poles.