What was Galileo's greatest scientific discovery?

In my opinion, his greatest discoveries were those about the nature of the solar system. His telescopic observations led to the start of a great revolution in the attempt to understand the nature of the objects in the sky. He discovered moons of Jupiter and the fact that Saturn has a system of rings.

He also corrected some misunderstandings about gravity. He proved that a pendulum's period was a factor of the length of the pendulum, not the length of the arc of the pendulum's swing. This led to pendulum clocks. He also postulated and proved that an objects rate of fall when dropped is independent of its weight. It had previously been assumed that heavier object fall faster than lighter objects by nature.


He also discovered the unwillingness of the Catholic Church to abandon superstitious dogma in favour of rational scientific thought.