1. Observation of Light and Shadow: Galileo noticed that the Moon's surface had areas that were brighter and darker. The bright areas were illuminated by the Sun, while the darker areas were in shadow.
2. Shape of the Shadow: The shadows cast by the bright areas were not perfectly round, but rather elongated and curved. This curvature suggested that the bright areas were not flat, but rather elevated or mountainous.
3. Changing Shadow Patterns: As the Moon progressed through its phases, the shadows cast by these elevated areas changed in size and shape. This further supported the idea of a mountainous lunar landscape.
4. Comparison to Earth's Features: Galileo compared the lunar features to mountains and valleys on Earth, which he was familiar with. He recognized that the Moon's surface had similar features, but on a larger scale.
In summary, Galileo's observations of the Moon's light and shadow patterns, along with his understanding of Earth's topography, allowed him to infer the presence of highlands on the Moon. His observations were groundbreaking and challenged the prevailing geocentric view of the universe.
