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>He concluded that the device was specifically designed to model "epicyclic" motion in keeping with the ancient Greek notion that celestial bodies moved in circ

>He concluded that the device was specifically designed to model "epicyclic" motion in keeping with the ancient Greek notion that celestial bodies moved in circular patterns, called epicycles. (This was pre-Copernicus, so the fixed point around which they moved was believed to be the Earth.) Slightly tangential, but the whole pre/post-Copernicus narrative seems unlikely to be true to me. At least I find it difficult to believe it wasn't until the 16th century that someone worked this out and everyone prior was of some woefully mistaken (yet suspiciously Christian-aligned) view that the Earth was the center of the universe.

robonerd 5y ago
Earth being the center of the universe makes a lot of sense in a naive way, it doesn't feel like the earth is moving. Sat in this chair, I feel as though I am at rest, and when I look at the sky long enough, I see that the stars are moving. And even with Copernicus's insight, he was still missing some key details which made it harder to believe he had the general idea right. Copernicus modeled the solar system using circular orbits, not elliptical orbits. To fit the observed data to this model, he needed epicycles, just as the geocentric model required.
- TheBlight 5y ago
  https://en.wikipedia.org/wiki/Aristarchus_of_Samos https://en.wikipedia.org/wiki/Aristarchus_of_Samos We even have record of someone reasoning this out of simple observations nearly 2000 years prior. This suggests to me it was known (at least by intellectuals) for a very very long time.
- cryptonector 5y ago
  What's funny about Copernicus not understanding that the planets orbits were elliptical is that it must have been clear that the moon's orbit around Earth is. The Antikythera mechanism models an elliptical orbit for it, so it must have been obvious. Now, it's not obvious that the moon's orbit around the Earth is like that of the planets around the Sun, but it doesn't take much imagination to think that orbits are similar in nature regardless of what is being orbited.
miltondts 5y ago
Yep, this narrative is highly questioned in this book: https://en.wikipedia.org/wiki/Lucio_Russo#The_Forgotten_Revolution https://en.wikipedia.org/wiki/Lucio_Russo#The_Forgotten_Revo... If I'm not mistaken, there is quite a bit of evidence that they knew the correct model was with the Sun in the center and they only used epicycles because it was easier to calculate with the tools they had (compass etc). EDIT: I think the argument is at section "10.12 Seleucus and the Proof of Heliocentrism" of the book.
- selimthegrim 5y ago
  This book is awesome if only because it made me realize that some of these ancients like Seneca were actually giant pompous twats.
- TheBlight 5y ago
  Interesting. Thanks for the link I'll check it out.
- whatshisface 5y ago
  There was no difference between heliocentric and geocentric models (except for philosophical arguments based on false premises) until Newton invented physics and the idea of planets spiraling around through space became clearly impossible due to inertia. Pre-F=ma there could not have been any way to know what was at the "center" because the conceptual tools for privileging a non-rotating frame of reference over rotating ones had not yet been developed. Also, a heliocentric model still requires epicycles if the orbits in the model aren't elliptical.
  - wolverine876 5y ago
    I've wondered about that: Why privilege that frame of reference? It seems more intuitive and easier to work with, but do we have a better reason than that?
    - whatshisface 5y ago
      In a rotating frame of reference, forces appear in the equations that are proportional to the distance from the center. They are the forces necessary to make an object which is stationary in a non-rotating frame go in a circle in the rotating frame. Those forces do not correspond to springs, gravitating bodies or any physical phenomenon, and are called "fictitious forces." Non-rotating frames of references make those forces go away, and that is why they're special.
selimthegrim 5y ago
Ibn Shatir had most of it right except the heliocentric part. Tusi contributed a step but didn't take the last conceptual leap.
YeGoblynQueenne 5y ago
The theory that the Earth was the center of the universe dates from at least the time of Ancient Greece and is probably more ancient. There's nothing Christian about it, in fact Christian scholars probably took the idea from Ancient Greeks, whom they revered (particularly the Platonists). There were certainly heliocentric models of the universe proposed before Copernicus, but Copernicus' one was the more well-developed. In some cases we don't even have a model, as such, just some third-hand accounts mentioning that someone thought the sun must be in the center of the universe. I suspect the most famous example of that is Aristarchos of Samos, for whose heliocentric theory we only know via a very brief and poorly detailed passage in Archimedes' The Sand Reckoner: You [King Gelon] are aware that "universe" is the name given by most astronomers to the sphere, the centre of which is the centre of the earth, while its radius is equal to the straight line between the centre of the sun and the centre of the earth. This is the common account (τά γραφόμενα), as you have heard from astronomers. But Aristarchus brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the "universe" just mentioned. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same centre as the sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the centre of the sphere bears to its surface. https://en.wikipedia.org/wiki/Heliocentrism#Aristarchus_of_Samos https://en.wikipedia.org/wiki/Heliocentrism#Aristarchus_of_S... So it's not that there weren't heliocentric models of the universe before Copernicus, just that they didn't really catch on, I guess.
- TheBlight 5y ago
  >There's nothing Christian about it My point was maybe this had something to do with why it "didn't really catch on." Given how viciously the idea was attacked by the Roman Inquisition as being heretical it was probably not the first time the church encountered the concept. IIRC, monks were the predominant scribes in the western world pre-printing press. If intellectual ideas didn't conform to religious canon they could've theoretically been nearly completely erased via censorship only to be "newly discovered" by Copernicus etc.
ngcc_hk 5y ago
The actual truth is not that heroic. But we want hero. The path is the church did accept we watch from earth but every heaven body revolve around the sun except us. Catholic use this model and very accurately beat the Muslim and the Hans (do not want to use chinese as the fight started in yuan dynasty, Mongolian and Tibetan etc are not Hans) in the Far East precisely of these tables based on actual observation. This comes from a guy x then his student called kepler pointed out … Newton use Kepler not just a Copernicus model only. The key is Copernicus is only partially right as the orbit is NOT as he said. It is not circular. and in fact he did not have the details and hence might as well not exist and might not affect the history. That is why his book is ok for many decades after publishing. It is only of the models. And not exactly right like others. the actual path is those who have calculation and a detailed accurate projection which Copernicus did not have. That revolve around the earth model worked. Not Epicircie. In truth even today if you observe the sky from earth you cannot just have a solar model. You have the earth factor as well (like the earth minor movement around its axis abd hence North Star change from vega to polar then back to vega). Just solar modal is not right. Now whilst the looking thru telescope did disturb the worldview. It does not matter. And it is the attitude of Galileo that is more an issue. The pope is his friend you know well before he is a pope. Teasing him as a joker does not work in those days. I am not saying C and G is totally wrong. I just say if they were more careful (like C publish his only after his death). And G accept the practical model of using sun as a centre based on actual observation and do not write satire … instead proposing a model that incorporates elliptical orbit, earth role etc but everything revolve around the sun except the earth (then do something about it gradually). Anyway that is not the history of hero we read. We want drama. We want …
adrian_b 5y ago
Some of the Ancient Greek philosophers believed that the Sun, and not the Earth, is in the center. For example Aristarchus of Samos and Seleucus of Seleucia. However, the main problem with most of the achievements of the Ancient Greek Philosophy is that, unlike for logic and mathematics, for theories about natural objects they did not have good methods to determine which of several alternative theories is right. So in the natural sciences there are a lot of questions about which some Ancient Greek philosophers have guessed the correct answer while others have guessed wrong. Now we know who was right and who was wrong, but at that time this was non-obvious and in most cases the popularity of the alternative explanations was determined more by the rhetoric skill of their supporters than by their agreement with the observations of nature. Even when the agreement with observations was actually checked, the methods of measurement were seldom precise enough to allow a non-ambiguous decision between 2 theories. This also applies to the heliocentric theory and the geocentric theory. Both theories had their supporters, but in the end the geocentric theory became the main theory for almost 2 millennia because it happened to be the theory chosen by Hipparchus and then improved by Ptolemy. Ptolemy made a more detailed kinematic model of the movements of the bodies in the Solar System, which agreed better with the observations of the planets than all the earlier models, so those were abandoned until Copernicus revived the heliocentric model.
- TheBlight 5y ago
  >so those were abandoned until Copernicus revived the heliocentric model. I'm skeptical the previous heliocentric ideas were truly organically abandoned. More on that in my other comment: https://news.ycombinator.com/item?id=30991734 https://news.ycombinator.com/item?id=30991734
- FastMonkey 5y ago
  I was going to make a similar comment, but you phrased it better than I could have. It's easy to say in hindsight that X knew Y, but there's a big difference between knowing something and just suspecting it. In fact, at the time the evidence for many models was equally strong. So, based on the limited available evidence of the day it actually would have been incorrect to believe too strongly in any model, even the one that we now know to be better than the others.
nestorD 5y ago
Here is a great write-up on the subject of the transition to the heliocentric model: https://tofspot.blogspot.com/2013/10/the-great-ptolemaic-smackdown-table-of.html https://tofspot.blogspot.com/2013/10/the-great-ptolemaic-sma... One key element is that heliocentric models where just not as good at making predictions. It took new data for them to finally get to a dominating position.
Natsu 5y ago
> At least I find it difficult to believe it wasn't until the 16th century that someone worked this out and everyone prior was of some woefully mistaken (yet suspiciously Christian-aligned) view that the Earth was the center of the universe. That was because we do not perceive the Earth moving, but we see the stars move. Nobody could answer objections like why we don't go flying off the Earth if it's spinning. Yet any idiot could take a ball, put a rock or something on it, spin the ball and show you what happens. Why is the Earth itself somehow different? It's like how they knew that stellar parallax should exist, but nobody could measure it, which caused heliocentrism to be lacking evidence for quite a long time because the stars are just that far away that it's tiny. If you go to the average person now, I think you'll find that most people who accept all this science can't even give full explanations for why.
fatbird 5y ago
There's actually a fairly simple explanation for why a heliocentric solar system wasn't superior in antiquity or when Copernicus introduced it: in both the Ptolemaic and Copernican models, the orbits are circular and require complex "epicyclic" motion to account for observation. A heliocentric model wasn't simpler and more obvious until Kepler introduced elliptical orbits, doing away with epicycles in the heliocentric model. Crucially, elliptical orbits didn't work for the Ptolemaic model. Suddenly, a heliocentric solar system seemed much more elegant and likely.
utopcell 5y ago
I agree with you that heliocentrism was a known model in ancient Greece [1], but I believe that the reference was with respect to the functionality of the device, for which we know for certain that it places earth at the center. [1] https://en.wikipedia.org/wiki/Aristarchus_of_Samos https://en.wikipedia.org/wiki/Aristarchus_of_Samos
cryptonector 5y ago
Epicycles were certainly a modelling technique for making predictions. They weren't much of a theory since there was nothing in epicycles about causation -- no explanation of why, just a model for what-where-when. I'm sure it must have occurred to more than one back then that the planets go around the Sun in elliptical orbits. The Antikythera mechanism even models the elliptical orbit of the moon around the Earth, so it's not farfetched that they could have figured out the rest. However, convincing all the right "authorities" of the copernican view back then would have been culturally very difficult.

robonerd 5y ago

Earth being the center of the universe makes a lot of sense in a naive way, it doesn't feel like the earth is moving. Sat in this chair, I feel as though I am at rest, and when I look at the sky long enough, I see that the stars are moving. And even with Copernicus's insight, he was still missing some key details which made it harder to believe he had the general idea right. Copernicus modeled the solar system using circular orbits, not elliptical orbits. To fit the observed data to this model, he needed epicycles, just as the geocentric model required.

TheBlight 5y ago
https://en.wikipedia.org/wiki/Aristarchus_of_Samos https://en.wikipedia.org/wiki/Aristarchus_of_Samos We even have record of someone reasoning this out of simple observations nearly 2000 years prior. This suggests to me it was known (at least by intellectuals) for a very very long time.
cryptonector 5y ago
What's funny about Copernicus not understanding that the planets orbits were elliptical is that it must have been clear that the moon's orbit around Earth is. The Antikythera mechanism models an elliptical orbit for it, so it must have been obvious. Now, it's not obvious that the moon's orbit around the Earth is like that of the planets around the Sun, but it doesn't take much imagination to think that orbits are similar in nature regardless of what is being orbited.

miltondts 5y ago

Yep, this narrative is highly questioned in this book: https://en.wikipedia.org/wiki/Lucio_Russo#The_Forgotten_Revolution https://en.wikipedia.org/wiki/Lucio_Russo#The_Forgotten_Revo... If I'm not mistaken, there is quite a bit of evidence that they knew the correct model was with the Sun in the center and they only used epicycles because it was easier to calculate with the tools they had (compass etc). EDIT: I think the argument is at section "10.12 Seleucus and the Proof of Heliocentrism" of the book.

selimthegrim 5y ago
This book is awesome if only because it made me realize that some of these ancients like Seneca were actually giant pompous twats.
TheBlight 5y ago
Interesting. Thanks for the link I'll check it out.
whatshisface 5y ago
There was no difference between heliocentric and geocentric models (except for philosophical arguments based on false premises) until Newton invented physics and the idea of planets spiraling around through space became clearly impossible due to inertia. Pre-F=ma there could not have been any way to know what was at the "center" because the conceptual tools for privileging a non-rotating frame of reference over rotating ones had not yet been developed. Also, a heliocentric model still requires epicycles if the orbits in the model aren't elliptical.
- wolverine876 5y ago
  I've wondered about that: Why privilege that frame of reference? It seems more intuitive and easier to work with, but do we have a better reason than that?
  - whatshisface 5y ago
    In a rotating frame of reference, forces appear in the equations that are proportional to the distance from the center. They are the forces necessary to make an object which is stationary in a non-rotating frame go in a circle in the rotating frame. Those forces do not correspond to springs, gravitating bodies or any physical phenomenon, and are called "fictitious forces." Non-rotating frames of references make those forces go away, and that is why they're special.

selimthegrim 5y ago

Ibn Shatir had most of it right except the heliocentric part. Tusi contributed a step but didn't take the last conceptual leap.

YeGoblynQueenne 5y ago

The theory that the Earth was the center of the universe dates from at least the time of Ancient Greece and is probably more ancient. There's nothing Christian about it, in fact Christian scholars probably took the idea from Ancient Greeks, whom they revered (particularly the Platonists). There were certainly heliocentric models of the universe proposed before Copernicus, but Copernicus' one was the more well-developed. In some cases we don't even have a model, as such, just some third-hand accounts mentioning that someone thought the sun must be in the center of the universe. I suspect the most famous example of that is Aristarchos of Samos, for whose heliocentric theory we only know via a very brief and poorly detailed passage in Archimedes' The Sand Reckoner: You [King Gelon] are aware that "universe" is the name given by most astronomers to the sphere, the centre of which is the centre of the earth, while its radius is equal to the straight line between the centre of the sun and the centre of the earth. This is the common account (τά γραφόμενα), as you have heard from astronomers. But Aristarchus brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the universe is many times greater than the "universe" just mentioned. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun on the circumference of a circle, the sun lying in the middle of the orbit, and that the sphere of the fixed stars, situated about the same centre as the sun, is so great that the circle in which he supposes the earth to revolve bears such a proportion to the distance of the fixed stars as the centre of the sphere bears to its surface. https://en.wikipedia.org/wiki/Heliocentrism#Aristarchus_of_Samos https://en.wikipedia.org/wiki/Heliocentrism#Aristarchus_of_S... So it's not that there weren't heliocentric models of the universe before Copernicus, just that they didn't really catch on, I guess.

TheBlight 5y ago
>There's nothing Christian about it My point was maybe this had something to do with why it "didn't really catch on." Given how viciously the idea was attacked by the Roman Inquisition as being heretical it was probably not the first time the church encountered the concept. IIRC, monks were the predominant scribes in the western world pre-printing press. If intellectual ideas didn't conform to religious canon they could've theoretically been nearly completely erased via censorship only to be "newly discovered" by Copernicus etc.

ngcc_hk 5y ago

The actual truth is not that heroic. But we want hero. The path is the church did accept we watch from earth but every heaven body revolve around the sun except us. Catholic use this model and very accurately beat the Muslim and the Hans (do not want to use chinese as the fight started in yuan dynasty, Mongolian and Tibetan etc are not Hans) in the Far East precisely of these tables based on actual observation. This comes from a guy x then his student called kepler pointed out … Newton use Kepler not just a Copernicus model only. The key is Copernicus is only partially right as the orbit is NOT as he said. It is not circular. and in fact he did not have the details and hence might as well not exist and might not affect the history. That is why his book is ok for many decades after publishing. It is only of the models. And not exactly right like others. the actual path is those who have calculation and a detailed accurate projection which Copernicus did not have. That revolve around the earth model worked. Not Epicircie. In truth even today if you observe the sky from earth you cannot just have a solar model. You have the earth factor as well (like the earth minor movement around its axis abd hence North Star change from vega to polar then back to vega). Just solar modal is not right. Now whilst the looking thru telescope did disturb the worldview. It does not matter. And it is the attitude of Galileo that is more an issue. The pope is his friend you know well before he is a pope. Teasing him as a joker does not work in those days. I am not saying C and G is totally wrong. I just say if they were more careful (like C publish his only after his death). And G accept the practical model of using sun as a centre based on actual observation and do not write satire … instead proposing a model that incorporates elliptical orbit, earth role etc but everything revolve around the sun except the earth (then do something about it gradually). Anyway that is not the history of hero we read. We want drama. We want …

adrian_b 5y ago

Some of the Ancient Greek philosophers believed that the Sun, and not the Earth, is in the center. For example Aristarchus of Samos and Seleucus of Seleucia. However, the main problem with most of the achievements of the Ancient Greek Philosophy is that, unlike for logic and mathematics, for theories about natural objects they did not have good methods to determine which of several alternative theories is right. So in the natural sciences there are a lot of questions about which some Ancient Greek philosophers have guessed the correct answer while others have guessed wrong. Now we know who was right and who was wrong, but at that time this was non-obvious and in most cases the popularity of the alternative explanations was determined more by the rhetoric skill of their supporters than by their agreement with the observations of nature. Even when the agreement with observations was actually checked, the methods of measurement were seldom precise enough to allow a non-ambiguous decision between 2 theories. This also applies to the heliocentric theory and the geocentric theory. Both theories had their supporters, but in the end the geocentric theory became the main theory for almost 2 millennia because it happened to be the theory chosen by Hipparchus and then improved by Ptolemy. Ptolemy made a more detailed kinematic model of the movements of the bodies in the Solar System, which agreed better with the observations of the planets than all the earlier models, so those were abandoned until Copernicus revived the heliocentric model.

TheBlight 5y ago
>so those were abandoned until Copernicus revived the heliocentric model. I'm skeptical the previous heliocentric ideas were truly organically abandoned. More on that in my other comment: https://news.ycombinator.com/item?id=30991734 https://news.ycombinator.com/item?id=30991734
FastMonkey 5y ago
I was going to make a similar comment, but you phrased it better than I could have. It's easy to say in hindsight that X knew Y, but there's a big difference between knowing something and just suspecting it. In fact, at the time the evidence for many models was equally strong. So, based on the limited available evidence of the day it actually would have been incorrect to believe too strongly in any model, even the one that we now know to be better than the others.

nestorD 5y ago

Here is a great write-up on the subject of the transition to the heliocentric model: https://tofspot.blogspot.com/2013/10/the-great-ptolemaic-smackdown-table-of.html https://tofspot.blogspot.com/2013/10/the-great-ptolemaic-sma... One key element is that heliocentric models where just not as good at making predictions. It took new data for them to finally get to a dominating position.

Natsu 5y ago

> At least I find it difficult to believe it wasn't until the 16th century that someone worked this out and everyone prior was of some woefully mistaken (yet suspiciously Christian-aligned) view that the Earth was the center of the universe. That was because we do not perceive the Earth moving, but we see the stars move. Nobody could answer objections like why we don't go flying off the Earth if it's spinning. Yet any idiot could take a ball, put a rock or something on it, spin the ball and show you what happens. Why is the Earth itself somehow different? It's like how they knew that stellar parallax should exist, but nobody could measure it, which caused heliocentrism to be lacking evidence for quite a long time because the stars are just that far away that it's tiny. If you go to the average person now, I think you'll find that most people who accept all this science can't even give full explanations for why.

fatbird 5y ago

There's actually a fairly simple explanation for why a heliocentric solar system wasn't superior in antiquity or when Copernicus introduced it: in both the Ptolemaic and Copernican models, the orbits are circular and require complex "epicyclic" motion to account for observation. A heliocentric model wasn't simpler and more obvious until Kepler introduced elliptical orbits, doing away with epicycles in the heliocentric model. Crucially, elliptical orbits didn't work for the Ptolemaic model. Suddenly, a heliocentric solar system seemed much more elegant and likely.

utopcell 5y ago

I agree with you that heliocentrism was a known model in ancient Greece [1], but I believe that the reference was with respect to the functionality of the device, for which we know for certain that it places earth at the center. [1] https://en.wikipedia.org/wiki/Aristarchus_of_Samos https://en.wikipedia.org/wiki/Aristarchus_of_Samos

cryptonector 5y ago

Epicycles were certainly a modelling technique for making predictions. They weren't much of a theory since there was nothing in epicycles about causation -- no explanation of why, just a model for what-where-when. I'm sure it must have occurred to more than one back then that the planets go around the Sun in elliptical orbits. The Antikythera mechanism even models the elliptical orbit of the moon around the Earth, so it's not farfetched that they could have figured out the rest. However, convincing all the right "authorities" of the copernican view back then would have been culturally very difficult.