Daniel keeps spinning a compass around in his hand. And every single time, the needle turns back.

No matter what he does. No matter which way he points it. The needle doesn't care.

So what's it actually feeling?

It turns out, the answer starts about 1,800 miles below your feet — deep inside the Earth, where there's an enormous layer of liquid metal, mostly iron, that's constantly swirling and churning. All that movement generates a magnetic field that stretches out through the ground, through the air, and all the way into space. The Earth isn't just a planet. It's a giant magnet.

And your compass needle is a tiny one. Magnets align with magnetic fields. So the needle turns until it lines up with the Earth's magnetic field — and that direction is what we call north.

Simple enough. Except it's not quite that simple. ...