Presentation: solar system motions

Galileo's observations of moons orbiting Jupiter. This did not necessarily disprove that Earth is at the center of motion in the solar system, but it made it much more plausible that Earth could move (around the sun) and not leave the moon behind, if Jupiter could move and not leave its moons behind.

The phases that Venus undergoes, which was also observed by Galileo. Note that Venus appears completely black when silhouetted against the sun as it passes between Earth and the sun, and Venus gibbous phases when it is going around behind the sun. This was the ultimate proof that Earth was not the sole center of motion in the solar system if Venus and other planets exhibit phases as they orbit the sun.