I once heard an astrophysicist on Radio 4 opine that if alien species did exist and had interstellar travel, like in science fiction, then Earth would be famous throughout the galaxy for its solar eclipses; beings would come as tourists to Earth to behold this marvellous cosmic coincidence: a single moon which is exactly the right size in the sky to cover the solar system’s sun, leaving just a tiny ring of light while all around, the sky goes dark