# Historical views about the revolution of the Moon

Copernicus and Galilei did away with Ptolemy’s belief that the Earth was at the centre of the Universe, and that all other celestial bodies (plus a concentric set of “spheres”) revolve around it.

But in one aspect Ptolemy actually was right, namely, the revolution of the Moon around the Earth. Was there ever any doubt about this in the history of astronomy? I’m wondering if there ever was a time when overzealous heliocentrics disputed this and postulated something else, such as a direct revolution of the Moon around the Sun.

That seems unlikely. Even with the naked eye it is easy to see that the same side of the Moon faces the Earth, and the phases of the Moon are readily explicable only if you assume it is orbiting (not rotating) about the Earth.

Stranger

Even Tycho’s alternate theory, which was a hybrid of Ptolemy and Copernicus, had the Moon orbiting the Earth.

The gravitational force of the Sun on the Moon is twice that of the Earth, and the Moon’s orbit is every concave towards the Sun. So in a sense it does orbit the Sun.

It’s the same sense that the Earth orbits the sun, by traveling around it.

I don’t think this is true. The Moon is not pulled toward the Sun away from the Earth. Both Earth and Moon are traveling at the “correct” speed to orbit the Sun at this distance if the other body were not there; with both bodies present the barycenter of the Earth-Moon system orbits the Sun. To the extent the Moon’s orbit is non-circular, the ellipse is not oriented consistently relative to the Sun.

What does your answer mean? It is true that the Moon is not pulled away from the Earth toward the Sun, and it is equally true that the Moon is not pulled away from the Sun towards the Earth, and follows a convex orbit around the Sun.

never mind

I said concave towards the sun, this site describes it as convex meaning the shape enclosed is convex. They mean the same thing.

The way you phrased your original post it appeared that you were claiming that the Moon’s orbit around the Earth was distorted by the Sun.

As for the exact shape of the Moon’s orbit around the Earth, well, that is a centuries-long rabbit hole

The Sun effects all sorts of crazy perturbations/distortions, a few of which were known in ancient times (e.g., evection), but to approach modern standards of accuracy you need thousands of terms.

The heliocentric model won out because it was a simpler explanation than the epicycles required to explain retrograde motion of the planets. The Moon with its very regular orbit never required such a simplification, so if anyone ever suggested it it would have been because they were absolutely terrible astronomers.

When looking at the available information to astronomers it’s not that surprising the geocentric model was the most popular for so long. The Moon obviously orbits the Earth in a nice patter. The Sun does the same. All the fixed stars do too. That there’s also a few “wandering stars” doesn’t seem like a reason to search for a “better” explanation until you get a telescope and discover how majorly different they are from the fixed stars.

And you start to see that they have moons of their own.