Nitpick: Actually, in most cases Copernicus’s system did fit the observations (and made predictions) somewhat better than Ptolemy’s: neither system was perfect, but neither was way off either. They could both be considered pretty good, given the limits of observational accuracy available at the time. (Although, in fact, both Ptolemy and Copernicus largely relied on data gathered well before their own time. Both made heavy use of the data gathered by Hipparchos of Rhodes, a couple of centuries before Ptolemy’s time and many centuries before Copernicus.)
Assessing which system was “more complicated” is not a very straightforward matter, and there is certainly much more to it than counting epicycles. (In any case, it is hard to say how many epicycles Ptolemy’s system involved, given that it had been tweaked and modified many times over the centuries. Versions in use by Copernicus’ time were usually different, in details, from teh model Ptolemy originally proposed.) There are other complications like eccentric points (which both systems employed freely), equants (which Ptolemy used freely, but Copernicus eliminated completely because, as you say, he had an aversion to irregular circular motion), and a new device that Copernicus introduced whereby Mercury slid back and forth along a short straight line at times. In general, though, because he got rid of the equants, Copernicus’s system was usually regarded as rather easier to handle mathematically.
Well, I don’t know about Ursus, but, to reiterate, for most people (certainly including Galileo’s religious critics) a rotating Earth would have been even more of a problem than an orbiting Earth. I do not see what problem (scientific or religious) would have been solved by a system with a stationary but rotating Earth. What would be the motivation for such a view? On the other hand, there was plenty of motivation for keeping the Earth completely still, as Tycho did.
Ursus may have proposed what you say, but I find it hard to believe that it ever had much significant support (unlike Tycho’s actual system, without rotation). Ursus would have been getting the worst of both worlds, Tycho looked, for a while, as though he could give you the best of both.
The real virtue of Copernicus’ system over Ptolemy’s was that even in its simplest form, it qualitatively accounted for all of the astronomical observations, including some that the Ptolemaic system never really addressed.
Specifically, one can easily qualitatively observe that:
1: Some planets always stay relatively close to the Sun in the sky.
2: The planets which do not stay close to the Sun occasionally move “backwards” relative to the background stars.
3: When a planet is doing this backwards motion (known as retrograde motion), it’s the brightest it ever gets.
4: When a planet is in retrograde motion, it’s opposite the Sun in the sky.
The simplest version of the Ptolemaic system can’t explain any of this. Even when you bring in epicycles, you can account for 2 and 3, but 1 and 4 remain unexplained quirks-- You can make the epicycles have that effect, but there’s no explanation of what the Sun has to do with anything. By contrast, the Copernican model in its simplest form, without any epicycles or other tweaks at all, can account for all four of these observations quite naturally.
Now, when you get into quantitative measurements of precise positions, and so on, neither model really works all that well, and has to be further tweaked. But at that simple level, Copernicus has a very definite advantage.
That is all true, but I do not think any of it played a very significant role in getting heliocentrism accepted. None of the facts that you list were the main things that convinced Galileo or Kepler (or Giordano Bruno), and it was the work of Galileo and Kepler (and, to a lesser extent, the ravings of Bruno) that actually eventually convinced people. Before their work, you could probably have counted the number of other people who actually believed that the Earth was in motion on the fingers of one hand.
Well, Galileo had access to his own telescopic observations, which most folks (including Copernicus) didn’t. And Kepler’s model wasn’t really Copernicus’, but a more sophisticated one which really did match the detailed quantitative data perfectly (and he also had the benefit of Tycho’s extraordinarily good observational data, which were better than anything Copernicus had).
Of course, they actually do, don’t they? I mean, Wikipedia says the Solar System orbits the galactic core at 220 km/s - that’s an astronomical unit every 8 days, which sounds pretty ludicrously fast to me.
I missed this before. No, the Ptolemaic system did not have a rotating Earth (for the reasons I gave in Post 18 - minus the Biblical ones). Yes, the stars would have to be moving pretty fast. Indeed, the planets (including the Sun and Moon) would all have to be moving pretty fast too, since the whole shebang was supposed to be circling the Earth once every 24 hours. After all, over the course of one day and night a planet will only have moved a tiny bit relative to the background of the stars; all those epicycles, defferents, eccentrics and equants were introduced to account for that tiny (and variable) bit of movement against this background.
But the speed of rotation did not seem ludicrous for several reasons. First of all, nobody really had much idea about the absolute distances involved, but it was generally assumed that the whole system was very much smaller than the Solar System as we now understand it, let alone the galaxy or the universe. In particular, the stars were thought to be all on the surface of a sphere, centered on the Earth, and not much further away than Saturn (which itself was not thought to be nearly as far away as it actually is). The smaller the whole system, of course, the lower the speeds involved.
Secondly, according to the Aristotelian system of physics, within the context of which the Ptolemaic astronomy was usually understood,* the heavens and heavenly bodies are made of a radically different sort matter from that found down here on Earth, with radically different properties and forms of motion (notably, Earthly matter naturally moves in straight lines, heavenly matter naturally moves in circles). No-one used to thinking in this way would have felt justified in extrapolating intuitions about what might constitute a “ludicrous” speed for Earthly matter into the realm of the heavens, where the nature of both matter and motion were conceived to be quite different. If the stars have to move very, very fast in order to get right round the Earth in one day, then so be it. That is just how star stuff is. (And after all, modern science tells us some pretty weird shit about star stuff even today.)
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*In fact, there are, arguably, inconsistencies between Ptolemaic astronomical theory and Aristotelian physics. For instance, Aristotle assumes that there are concentric crystalline (i.e., transparent) spheres that move the planets around in their orbits. (They do not hold the planets up. Planets do not need to be held up. They are not made of the sort of stuff that tends to fall down.) It rather looks as though Ptolemaic epicycles, if real, will require spheres to intersect one another. In practice, through antiquity and the middle ages this problem did not worry many people because the Ptolemaic theory was taken to be a mere calculating device, and not taken very seriously as a description of physical reality. If you wanted to know about the physical reality of the heavens you asked the philosophers (who were mostly Aristotelians - who also believed in an unmoving Earth, of course); you would only ask the mathematical astronomers, who based their work on Ptolemy, if you wanted precise predictions about the future positions of the planets, almost always for astrological purposes. (Math, in those days, tended to be associated with mysticism and superstition, not rationality.) However, the inconsistency between Ptolemaic astronomy and Aristotelian physics did apparently become a worry for some people in the 16th and 17th centuries, and probably did play some role in the eventual acceptance of both heliocentrism and the new physical theories that were largely designed to be consistent with it.
I’m reasonably sure that I have heard of Archimedes objecting to a non-rotating Earth on the grounds of the ludicrous speeds of the stars… But I don’t think I can find a cite, so I’ll let the matter drop.
That is possible. I am not saying that nobody in the ancient world ever raised the idea of a rotating Earth. Someone probably did, as, apparently, Ursus did in the 16th century, and maybe Archimedes did. Maybe he also made this argument (of course, people are bound to differ over what they consider “ludicrous”). What I am saying, however, is that, for good reasons, a rotating but otherwise stationary Earth was never part of any widely accepted, or even very widely debated astronomical theory, such as that of Ptolemy or that of Tycho.
There were several scientists (e.g. Heraclides, Oresme, Alhazen, and poss. Aryabhata and Biruni) who accepted daily rotations before Copernicus.
There may have been variants of the Tychonic system in ancient Greece, some with only the inner planets revolving around the Sun, with Sun and outer planets revolving around Earth. And of course Aristarchus proposed heliocentrism 1800 years before Copernicus. (This is known through Archimedes’ writings though AFAIK Archimedes never gave his opinion on the matter.)
The complicated Ptolemaic system may have required great mathematical ingenuity. I wonder if that ingenuity set back science!