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The development of telescopes enabled the discovery of moons orbiting around Jupiter, and the existence of a full set of phases of Venus, as opposed to a limited set which would be predicted by geocentrism.

But is it possible to disprove, or at least make implausible, geocentrism without a telescope? Preferably without calculus or more advanced maths.

I'm curious for two reasons. One is knowing whether it was lack of technology, or humanity's attitude towards the universe, that was responsible for geocentrism. The other is that I've heard that some astronomical facts, such as the size of the earth, were calculated before the advent of telescopes, and I'd find it interesting if more facts could have been deduced even with a limited set of technology.

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  • $\begingroup$ Funny thing is that Galileo discovered physical epicycles of sorts. The Jovian moons cycle around the orbit of Jupiter. I don't know if this confused people at the time. $\endgroup$
    – LocalFluff
    Commented Feb 1, 2015 at 22:55

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I would argue that the Apparent retrograde motion of the planets over time, is evidence against geocentrism, and probably why Aristarchus of Samos proposed a Heliocentric model of the Solar System.

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  • $\begingroup$ You can just brush this away by coming up with epicycles. $\endgroup$
    – HDE 226868 ♦
    Commented Feb 1, 2015 at 0:45
  • $\begingroup$ @HDE226868 Even then, at least if you insist on circles instead of ellipses, you have to assume that all planets orbit an empty place in space next to Earth, not Earth proper. Even Copernicus was not heliocentric, according to him everything orbited an empty place in space next to the Sun. The Sun was just a non-physical decoration on his sky. $\endgroup$
    – LocalFluff
    Commented Feb 1, 2015 at 21:55
  • $\begingroup$ @LocalFluff Then you can still postulate that they orbit in ellipses. That should solve the problem. I understand what you're getting at, though. $\endgroup$
    – HDE 226868 ♦
    Commented Feb 1, 2015 at 22:30
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You can't disprove geocentricism. It is a perfectly valid way to look at the universe. After all, all frames of reference are equally valid.

What you can disprove is that geocentricism is the one and only way to look at the universe. Once again, all frames of reference are equally valid. This means that a Highlander point of view ("in the end, there is only one") is nonsense, which in turn means that claims that geocentricism is the one and only valid point of view is nonsense.

That all frames of reference are equally valid does not mean that frame X is just as good as frame Y when it comes to explaining motion. Frame Y might well need a slew of fictitious forces while frame X needs none. The absence of fictitious forces in frame X makes the equations of motion take their simplest form when viewed from the perspective of frame X. Other frames of reference such as Frame Y (e.g., geocentricism) will result in fictitious forces. These fictitious forces vanish with a smarter choice of reference frames.

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  • $\begingroup$ Hee, here's actually a Lunar astronomer who uses a geocentric model because it is "convenient"! $\endgroup$
    – LocalFluff
    Commented Feb 2, 2015 at 17:13
  • $\begingroup$ @LocalFluff - He's confused. He is not using a Ptolemaic point of view. The Ptolemaic point of view is Earth-centered, Earth-fixed (ECEF). That's what weather forecasters (amongst many others) use. I challenge you to use anything but for weather forecasting. Matija Cuk in that video is using a so-called Earth-centered inertial (ECI) point of view. The Earth rotates. He specifically said so; the Earth was rotating very quickly way back then. $\endgroup$
    – David Hammen
    Commented Feb 2, 2015 at 23:55
  • $\begingroup$ @DavidHammen: If your model of the Earth has no fictitious forces, how do you explain hurricanes, without appealing to something resembling Coriolis? $\endgroup$
    – Kevin
    Commented Jun 1, 2022 at 4:24
  • $\begingroup$ @Kevin Explaining the weather from an Earth-centered inertial frame is a pain in the rear, but it is possible. It's possible to explain the Earth's weather from the perspective of a Moon-centered, Moon-fixed (MCMF) perspective. All frames of reference are equally valid. Some perspectives are easier to use than others. An Earth-centered, Earth-fixed (ECEF) is the easiest frame for explaining the Earth's weather, despite the fictitious forces that arise, because the Earth's atmosphere rotates more or less in sync (but not exactly in sync) with the solid Earth. $\endgroup$
    – David Hammen
    Commented Jun 1, 2022 at 7:08
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Johannes Kepler actually disproved geocentrism only a few years before the telescope was invented. He used Tycho Brahe's surprisingly precise naked eye observations of Mars' and the Sun's relative positions on the sky. He first proved that Ptolemy's, Copernicus' and Brahe's Solar system models were all mathematically identical, they just chose different frames of reference. Then he painstakingly founded astrophysics and proved genuine heliocentrism.

Here's a free online study guide for Johannes Kepler's work "New Astronomy", with some interactive java animations. He was a contemporary with William Shakespeare, so it should not come as a surprise that he was pretty easy to read (in English translation, first available only in the 1980's!) for being a 400 years old astronomer, making personal comments and even some jokes between the lines.

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