Earth is a planet in general, but the human knowledge that this point is in the 16th century, after the Copernican heliocentric theory put forward.

Dear Copernicus: I'm a was reading of the students, I think you the heliocentric theory of gravitation is, I hope very much to you can publish your own ideas.

The achievement in astronomy was the revival and proof of the heliocentric theory that is regarding the sun as center.

This is a simplified model for showing the same observation in geocentric model and heliocentrism. Blue ball means Earth.

But in a world in which, according to Vermij, the Tychonic system was regarded as a serious rival of the Copernican system, Marius's conclusions seem reasonable.