Supernovae are the most powerful explosions in the universe, unleashing enough energy to outshine galaxies. We have no real metaphor for their power – if the sun were to magically go supernova it would feel like you were being hit by the energy of a nuclear explosion, every second. For weeks. While supernovae are the engines of creation, forging the elements that enable life, they also burn sterile whole regions of galaxies. So what would happen if one hit earth?