the ancient Greeks weren't satisfied with this sort of fantasy. some wanted to know what the spots actually were. one idea was that they were reflections of the Earth's continents and seas. But others showed that this was not possible. Pluto of Chaeronea, a Romanized Greek who lived from about 46 to 120 CE, wrote a book titled on the face of the disk of the Moon. He reported a wide variety of opinions about the moon and gave arguments for and against each. He refuted some of those theories, such as the one that the markings were illusions in the eye of the beholder. Instead he suggested, rightly, that the light and dark areas are composed of different materials. He demonstrated that the moon's phases prove it to be a solid, opaque sphere with a rough surface lit by sunlight, an object very much like the Earth. Extending this analogy, he declared that the moon was covered with mountains and valleys. This very correct idea may have been suggested by the small irregularities that can be seen in the moon's straight edge near its quarter phases. They are indeed shadows cast by lunar mountains.