 Having dispelled these arguments against the Copernican system, Galileo then dramatically argues in its favor. In Day Three of the Dialogue. Salviati, Galileo’s avatar, has Simplicio, the ever-astounded Aristotelian, make use of astronomical observations, especially the facts that Venus has phases and that Venus and Mercury are never far from the sun, to construct a diagram of the planetary positions. The resulting diagram neatly corresponds to the Copernican model. Then in Day Four, Galileo offers a supposed proof of Copernican theory on the basis of the tides, asserting that they result from the combination of the Earth’s diurnal rotation and its annual motion around the sun.