And Alduin can eat planets. He's the son of a god. And gods in Elder Scrolls aren't like gods in Warcraft. A lesser god had so much power, that when he moved at his maximum speed it tore a hole in reality. This hole is what normal people call the sun. Alduin himself is also a god, representing the anti-pantheon to the Nine Divines. He is the World Eater and the Nordic God of Destruction. Alduin destroyed the previous world.
Did I mention Alduin is immortal?