How did the observation of illuminated peaks contrasted with dark valleys help Galileo deduce lunar topography?

Answer

This phenomenon was analogous to the illumination of Earth's mountains during sunrise or sunset.

The pattern where high points catch light while low areas remain shadowed precisely mirrors how light interacts with mountains and valleys on Earth, strongly suggesting the Moon possessed similar features.

How did the observation of illuminated peaks contrasted with dark valleys help Galileo deduce lunar topography?
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