"In Leonardo's time, most people believed that the Moon - like all celestial bodies - was a perfect, unblemished sphere which shone with its own light. However, Leonardo noticed that the Moon did not look uniform. He also realised that when it was low in the sky, you could sometimes see the whole of its round surface faintly, even when only a thin crescent was lit.Leonardo decided that the Moon itself did not shine with its own light, but reflected the light of the Sun. Although he was not the first person to suggest this, it is a perfect example of how he was willing to trust his own observations over conventional wisdom.Leonardo also realised that if you were standing on the surface of the Moon, then the Earth might appear as the Moon does to us. He also suggested that it might be covered with water, and that the markings seen from the Earth were caused by giant waves on the surface. Clearly this last idea was wrong. However, his understanding of the Solar System was one of the most advanced of the age."

Leonardo Da Vinci