How did Galileo use the Earth’s moon to support the Heliocentric model??

I am not familiar with any study that claims such a thing. It was the Jovian satellites (Galileo’s discovery) that lead to confirmation of something orbiting something other than the sun. It also led to the discovery of light taking time to travel form one point to another, and eventually, the speed of light.

I cannot find a source that claims that Galileo ever used earths moon to make such a determination. May I inquire as to your source?

Hi Michael!

Galileo’s observations of the moon tended to support the heliocentric theory in an indirect way.

Galileo owned the best telescope in the world at that time. When he pointed it to the moon, he was able, for the first time, to see mountains and craters. He could make out shadows on the lunar surface.

The unexpected thing about lunar mounatins was not so much that they cast shadows. That could easily have been predicted from Ptolemy’s theory, that the earth is in the center and everything revolved around us.

Rather, it was the very fact of surface features at all. Most people imagined that celestial bodies were perfect, or at least quite unlike earth. This, it was supposed, is what makes earth different. When Galileo demonstrated that the moon has mountains and rough terrain like the earth, he showed that there was no longer a reason for anyone to think earth unique.

In other words, by his observations of the moon, he indirectly supported the heliocentric model.

By the way, several of Galileo’s ideas were mistaken, which is why they did not gain immediate acceptance. For instance, he posited that the tides are caused by the earth’s motion around the sun, not by the moon. The entire body of his work did, eventually, give compelling support for the modern heliocentric theory.

I believe he used the phases of Venus to prove the Heliocentric model. By showing Venus phases which could only happen if Venus circled the Sun.