101: Spin Down Earth

The Earth's core has been acting weird for at least 70 years now. We're not sure why, but sometimes it's spinning faster than the surface, sometimes slower. Emily explains how we know what's happening down in the core, which is impressive enough ... but then she shows how astronomers do the same for very distant stars, and Chris's head explodes. Plus, it's been a big week for aurora fans, and there's even some bonus Einteinian weirdness at the end.