It's important to understand that Galileo didn't *invent* the theory that the Earth spins and orbits the sun. This idea was already proposed by Nicolaus Copernicus in the 16th century with his heliocentric model.

Galileo's contributions were:

* Observational evidence: He used his telescope to make observations that supported Copernicus's theory. He observed the phases of Venus, which could only be explained if Venus orbited the Sun, not the Earth. He also saw the moons of Jupiter, which demonstrated that not everything orbits the Earth.

* Public advocacy: Galileo publicly defended the heliocentric model, which was controversial at the time. He wrote books and engaged in debates with opponents, spreading awareness of the theory.

Therefore, it's more accurate to say that Galileo provided strong observational evidence for the Copernican theory and played a significant role in promoting its acceptance.

He did not come up with the theory himself, but rather, provided evidence and championed the work of Copernicus.