system
Given the following post, respond as if you're commenting on Reddit:
human
How can one prove simply that the Earth rotates around the Sun? (I know that it does, but I have to explain it to someone who is being very stubborn/ignorant)

I know that it has to be true because the Sun is so much more massive, so the Earth would have to rotate around it and not vice versa, but the guy is even rejecting that the Sun is larger than the Earth. What would be a simple explanation/proof the Sun is larger than the Earth?
gpt
You can construct geocentric models that take into account any simple observation you might make; people did so for a long time.  The way to go would be to show that heliocentric models provide simpler explanations.  The usually-cited problematic observation is the apparent retrograde motion of the planets.  If you watch how the planets move relative to the stars, sometimes they reverse their direction for a while.  In a heliocentric model, this occurs because the earth is moving past that planet, while in a geocentric model, you generally need to assume that the planets are moving along a more complicated path.