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Comment by lupire | Hacker News Reader

I'd think that the Earth rotating would be obvious much, much sooner, since that's far less work than the entire universe orbiting around the Earth every day, while also having individual objects orbiting on their own monthly, annual and other cycles. And spinning tops are common toys.

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Keep in mind that there was nothing indicating that the sun and the stars were of the same nature, or that they were so far away. When you think about it, all stars appear equally distant to the naked eye, so the idea that stars were fiery stones dispersed on a vast celestial sphere was absolutely plausible. This solid, physical sphere was the thing rotating.

Also people had little understanding of the scale of things. There is nothing indicating that the moon is smaller than earth or that the sun is much, much bigger than earth, and both appear equally large in the sky...

> Also people had little understanding of the scale of things. There is nothing indicating that the moon is smaller than earth or that the sun is much, much bigger than earth, and both appear equally large in the sky...

The Ancient Greeks were actually quite clever about trying to calculate things:

* https://physicsteacher.blog/2021/05/31/from-the-earth-to-the...

* https://en.wikipedia.org/wiki/On_the_Sizes_and_Distances_(Ar...

* https://en.wikipedia.org/wiki/On_Sizes_and_Distances_(Hippar...

> I'd think that the Earth rotating would be obvious much, much sooner […]

How exactly could you tell the difference between one moving reference and another? Einstein eventually showed us that it is not possible.

As this US Navy video shows, having the Earth stand still and having the 'celestial sphere' move actually makes celestial navigation using a sextant possible / mathematically easy:

* https://www.youtube.com/watch?v=UV1V9-nnaAs / https://www.youtube.com/watch?v=cun0DGZ6-sk

The Ancients / pre-Moderns concluded that the stars were on one celestial sphere and the wanderers (planetes in Greek) were on others.

Einstein did not show that. The principal you are referring to is, ironically, Galilean relativity, and attributable to Galileo. Einstein's contribution was combining the principle of relativity with a constant speed of light.

Additionally, under both systems, relativity only applies to intertial reference frames. Rotating reference frames are detectable.

You can detect Earth's rotation without any external observations using a pendulum. Although such an experiment would not be done until Léon Foucault about 2 centuries after Galileo.

You can tell the difference between rotating and not, because a rotating reference frame is not inertial. In fact, the geocentrists knew this, because one of the longest-standing objections to the idea that the earth rotated was that you would expect a falling object to be displaced from the apparent vertical due to the rotation, these experiments were done, and the displacement was not observed (it turns out, because the effect was so small, but no-one would have the mathematical tools to work this out until Newton).

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