What did Galileo Galilei deicover?

Answer 1

Galileo discovered the four main moons that circle Jupiter, the telescope and backed up the coppernican theory that the planets rotate around the sun.

Answer 2

Galileo Galilei discovered that the Earth revolves around the Sun, not the other way around. This was a groundbreaking finding that supported the heliocentric model of the solar system proposed by Copernicus. Galileo's observations through his telescope also led to discoveries such as the moons of Jupiter and the phases of Venus.