Hacker News Reader

I tl;dr'ed the article (sorry), but I wanted to say one thing about epicycles. They are not wrong and certainly can be used to explain motion, but the problem with them is that you can keep adding epicycles to fit any continuous orbit at all (this actually is because a Fourier series can converge to any continuous periodic function). This is my favourite visualisation of this fact:

https://www.youtube.com/watch?v=QVuU2YCwHjw

View on HN

Exactly. From a geocentric perspective, it's not wrong as long as you're explaining past events (which, as you noted, can be done by adding epicycles).

The reason the model is not so useful (to paraphrase my college physics professor) is that you can't use it to predict things in advance with reasonable certainty (i.e. you don't know what epicycles you need until after you've observed it).

And, in fact, modern astronomers still use epicycles when studying Galactic orbits.

Reply on news.ycombinator.com