Did you know that compasses don’t actually point true north?
Compasses work by sitting tiny magnets on top of needles. When the needle is placed on a platform with very low friction, it spins to align with the earth’s magnetic field and point towards a pole.
If you have a compass, try holding it vertically so that the compass face is at a 90° angle to the ground. The needle will point into the ground, towards magnetic north: the closer you are to the north pole, the smaller the angle between the Earth’s surface and the needle. At the magnetic north pole, the compass needle will point directly downwards. (Here’s a video of a compass spinning randomly at the north magnetic pole.)
But the earth’s magnetic field doesn’t actually line up perfectly with the globe. In fact, the earth’s magnetic field shifts around quite a bit! The north magnetic pole is the point where earth’s magnetic field points vertically downwards toward the centre of the earth. It’s about 500km south of the geographical north pole. (The south magnetic pole is over a thousand kilometres away from the south pole).
In recent decades, the north magnetic pole has been moving faster and faster away from geographical north. Eventually, the poles will flip, so magnetic north is in the south, and vice versa. This is causing difficulties for navigators in the Arctic Ocean, but the differences don’t have much of an effect on anyone further away. In the Southern Hemisphere, our compasses should be pointing straight for a long time yet!
If you’re keen to do more magnetic science, here’s a compass you can make at home.
If you’re interested in mapping or earth sciences, you should check out the Bachelor of Applied Geographical Information Systems, the Bachelor of Science (Geography), or the Environmental Geology major in the Bachelor of Science.