is there any software library that calculates earth/moon/sun/planets positions based on the geocentric model?

if that exists, why is the heliocentric model the most popular?

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    $\begingroup$ Claudius Ptolemy did have such a model, a long time ago. That model was tossed by Nicolaus Copernicus, Galileo di Vincenzo Bonaiuti de' Galilei, Johannes Kepler, Isaac Newton, Albert Einstein, along with others. $\endgroup$ Commented Sep 28, 2022 at 9:10
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    $\begingroup$ The heliocentric model is most popular because it is correct $\endgroup$
    – Rory Alsop
    Commented Sep 28, 2022 at 13:44
  • $\begingroup$ When you say "The geocentric model" which one do you mean. There were many developed, mostly adding a tweak here or there to make the predictions more accurate. The best known one is that of Ptolemy but there were lots of others. So which geocentric model are you asking about? $\endgroup$
    – James K
    Commented Sep 28, 2022 at 19:33
  • $\begingroup$ The heliocentric model isn't really the defacto model either, the most accurate models are n-body simulations where no body is the center. The idea of kelperian orbits are simplifications that make visualizing easier, but are not that accurate. $\endgroup$ Commented Sep 28, 2022 at 22:13
  • $\begingroup$ I don’t know of any such library. As Rory Alsop points out, the heliocentric model is correct, while the geocentric one is not. Contrary to what Paul Garrett mentions, though, NASA’s model is not geocentric, even though it does allow geocentric coordinates to be determined. I have recently translated Ptolemy’s Almagest to French, including some animations. I could probably provide you with some useful code of a geocentric model, even though it’s wrong and imprecise because that’s not how nature works. $\endgroup$ Commented Sep 29, 2022 at 1:14

2 Answers 2


I don't know any software library which does what you require. But there is an account of the geocentric model in terms of modern mathematics (vector algebra etc) written by Professor Richard Fitzpatrick of the university of Texas. It is called "A Modern Almagest. An Updated Version of Ptolemy's Model of the Solar System" and available in html or pdf at: https://farside.ph.utexas.edu/books/Syntaxis/Syntaxis.html The procedures described in this book can be used to develop such a software library.

As we know today from the works of Copernicus and his successors the heliocentric system is the right one and describes the motion of the earth/moon/sun/planets very precisely.

Kind Regards Klaus


I think no one claims that assuming the earth is at the center of everything makes orbit predictions impossible. (For that matter, the apparent homogeneity of the cosmic background radiation seems to suggest that there is no "center" of the universe, etc.) It just makes things messier. That's partly why "local" problems like getting a spaceship to the moon, or to Mars, that do need to refer to Earth as a "ground point", become crazy, in comparison to two-body or restricted three-body problems.

But/and, yes, NASA in-effect has software that does such computations for Earth-to-X stuff!

That (also!) does not mean that the Earth is anywhere near the center of mass of the solar system. The sun is. And our solar system is nowhere near the center of mass of our galaxy. And ...

So, in some regards, the whole question of geocentric versus heliocentric doesn't really have content... at least insofar as there is no center, anyway, ... That kind of thing.

EDIT: the Community Bot has made some well-intentioned "suggestions" about editing-to-improve. Ok. But I am inclined to think that my minor reframing of the question answers it better than a literal response. Sure, opinions vary...

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    $\begingroup$ As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Commented Sep 28, 2022 at 22:59

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