Seeing is believing, but we do not see with our eyes only. We look at the world with the aid of inherited images that we may strive to improve but that we do not work to replace unless something dramatic occurs. The traditional Earth-centred system was confirmed not just by the everyday experience of seeing the Sun rise and set, but by the high-powered geometry that was embodied in Ptolemy’s Almagest, the result of centuries of diligent observation and detailed computation. Anyone who opens that great classic today cannot fail to be impressed by the mathematical sophistication that is displayed on virtually every page. Better still, those who use the Ptolemaic methods to determine the position of the planets find that they work. Indeed, elementary astronomy is still presented from the standpoint of a motionless Earth, and we learn to calculate where Venus or Mars will be in the night sky on the assumption that the celestial vault revolves once every twenty-four hours. We know, of course, that this is a fiction, but it remains a convenient fiction. It would not merely be pedantic, but foolish, to correct people who say that the Sun moves from east to west by pointing out that it is really the Earth that rotates from west to east. If you doubt this, try playing the rigorous astronomer at the next cocktail party. You may well discover that people are neither impressed nor amused.