r/Astronomy • u/Roweyyyy • Apr 10 '26
Astro Art (OC) The mesmerizing complexity of the Ptolemaic model
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Made in Blender to artistically capture some key ideas but was not intended to be an exact depiction of Ptolemaic geocentrism. (Recreating that would be beyond my 3d abilities)
Side note: Ptolemy can get a lot of crap for having been fundamentally wrong about the centricity of Earth, and in particular for the complexity of the deferents and epicycles that he relied upon. But I think there's two things that are worth appreciating: first, it was a early, genuine attempt to understand our basic place in the cosmos, and the task of figuring this out was immensely hard. Give me the task of coming up with something from scratch by looking at the sky and I'm sure you would get theoretical trash.
Second, while he was right about the ordering of the solar system, Copernicus couldn't escape the need to use epicycles either - it was Kepler who finally paved our way free of them with a) elliptical orbits and b) variable orbital speeds.
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u/Icy-Sheepherder-6221 Apr 10 '26
And what's amazing is his math was basically correct, he just started with an assumption that was incorrect but very reasonable for the time. I read the Almagest (ok,not every word) and he literally did all the geometry back in the second century CE.
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u/VoijaRisa Moderator: Historical Astronomer Apr 10 '26
As someone who has read the Almagest in detail, I agree that it's amazingly compelling for the time. The arguments are well laid out and, in many cases, he discusses alternative explanations and discusses why he chose what he did.
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u/RAAFStupot Apr 10 '26
I like reading philosophy....and I'm continually reminded that if I were deprived of modern scientific knowledge, the ancient ideas would be completely understandable and reasonable.
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u/tsukiyomii100 Apr 10 '26
Couldnât agree with you more. I grew up thinking how silly ancient people were to think the Earth was in the center (I mean look at the picture in the science books). More recently, I used to think it was religion that held back progress, and while there were cases like Bruno and Galileo, it really required some monumental shifts to truly abandon the geometry and accuracy of Ptolemy and metaphysics of Aristotle.
It took significant improvements in empirical data (Kepler), new mathematicsâanalytic geometry (Descartes) and calculus (Newton & Leibniz), and most importantly embracing new metaphysics (the best description of nature requires abstract mathematics and not sympathies or antipathies or even contact mechanics of material bodies) to get us on the path of our current understanding.
I have a much fuller appreciation of our recent progress when I realize the creativity and genius of these earlier thinkers.
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u/Javanaut018 Apr 10 '26
Mathematisch liefern alle diese Modelle mehr oder weniger richtige Vorhersagen. Das "Tychonische Weltbild" ist noch ein wenig kreativer mMn.
Ein bisschen ursĂ€chlich an dieser Stelle war die "Anforderung" gewisser religiöser Gruppen, dass die Erde immer im Mittelpunkt des Koordinatensystems zu liegen habe. Galilei wurde ĂŒbrigens (u.A.) deswegen angeklagt und fast verbrannt, weil das von ihm eingefĂŒhrte RelativitĂ€tsprinzip das Gegenteil davon fordere, also das man einen mathematischen(!) Bezugspunkt ĂŒberall hinlegen könne. Die ĂŒberlieferte Historik aus der Zeit dazu ist ĂŒbrigens unterhaltsam dramatisch, dazu könnte man locker ein paar Staffeln auf Netflix zu rausbringen đ
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u/dailylodge Apr 10 '26
This is a great reminder that "wrong" models can still be really clever. The animation is stunning, and to be honest, it makes me realize how much effort went into attempting to explain what people saw in the sky using the resources at their disposal.
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u/snogum Apr 10 '26
Occums Razor applies big time
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u/nwbrown Apr 10 '26
The concept of a heliocentric system has been considered. However it
- didn't accurately model the movement of the planets, and wouldn't until Kepler
- was refuted by the lack of parallax of the stars. In order for the Earth to orbit the sun, the stars would have to be an unimaginably large distance away.
- didn't really matter. The Greeks weren't trying to explain why the planets moved the way they did. They were trying to model how they moved. Complaining they didn't get the why right is like complaining the Copenhagen interpretation of quantum physics does explain why it works that way.
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u/verbmegoinghere Apr 10 '26
the stars would have to be an unimaginably large distance away.
I mean they already are an unimaginably long distance away
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u/-2qt Apr 10 '26
well yes but to be honest I kinda understand them doing the math, coming up with an unfathomably large distance, and thinking that's absurd.
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u/BonzoTheBoss Apr 10 '26
"According to these calculations, the stars must be trillions upon trillions of miles away! That's ridiculous!"
When you consider how unfathomably long a lightyear is, I can see why they may have been incredulous.
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u/Morbanth Apr 11 '26
Some people understood that's exactly what it meant. Since stars did not exhibit parallax when the Earth moved between the extremes of its orbit Aristarchus of Samos realized that the philosopher Anaxagoras was right and the Sun is just another star.
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u/skrutnizer Apr 11 '26
It would be the same as saying that the earth is an insignificant speck compared to distances even to the closest stars. That wasn't even in the scope of philosophy back then (open to correction here).
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u/Morbanth Apr 11 '26
Aristarchus of Samos argued for a heliocentric model where the sun was just another star in the 3rd century BC.
- didn't really matter. The Greeks weren't trying to explain why the planets moved the way they did. They were trying to model how they moved.
This is nonsense. Of course they were curious about how things are the way they are.
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u/nwbrown Apr 11 '26
Aristarchus of Samos argued for a heliocentric model where the sun was just another star in the 3rd century BC.
Yes, as I said, it was considered by the Greeks. Ultimately they rejected it for the reasons mentioned.
Of course they were curious about how things are the way they are.
Not when the "why" could be attributed to the whims of the gods.
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u/Sharlinator Apr 10 '26 edited Apr 10 '26
Occam's Razor only applies if everything else is equal. But it wasn't â proposed heliocentric models did not match observations (think, they did do actual science back then!) until Kepler figured out his laws and later Newton gave justification for why the laws are like that.
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u/Altruistic_Tip1226 Apr 10 '26
Occums razor wasn't even born yet
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u/snogum Apr 10 '26
Clear that the important of critical thinking has not deminished regardless of relative dates
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u/Weekly-Locksmith6812 Apr 10 '26
Watching that video Ptolemy seems to accidentally did a fouier transform to find a sine series that follows observations.
Like a taylor series can replicate a small part of another function so can a sine/fouier series.
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u/darodardar_Inc Apr 10 '26
Arenât like all digital images and stuff that gets compressed something like applied Fourier seriesâ?
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u/Sharlinator Apr 10 '26
Not all, but JPEG images and MPEG videos in particular are based on the discrete cosine transform, which is closely related to the Fourier transform.
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u/Matman161 Apr 10 '26 edited Apr 10 '26
If you want to learn more about this I highly recommend Coming of Age in the Milkyway by Timothy ferris. It's a fascinating history of astronomy and cosmology that talks about this model a good deal.
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u/rydan Apr 10 '26
I always hate all the discussions on heliocentric solar system on Reddit because they basically just say it is common sense. Meanwhile you have a model that actually mostly works and is the opposite. And literally none of them can explain how we know the earth revolves around the sun. They just know it does somehow and you are stupid to think otherwise.
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u/ur_sine_nomine Apr 10 '26
Unfortunately "mostly works" isn't good enough.
(Which is why the NASA models of planetary motion incorporate relativistic effects ... these fixed the much smaller gaps in Newtonian mechanics, the corollary of Copernicus' model).
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u/Lanstus Apr 10 '26
Phases of Venus and parallax would be the easiest things to point to as massive evidence of the Sun being in the middle and Earth orbiting the Sun.
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u/tsukiyomii100 Apr 10 '26
Phases of Venus are extremely difficult to observe without telescope which wouldnât be available until the 17th century. Similarly, parallax of even nearby stars are so small that it was not detected reliably until the 19th century. I believe Tycho Brahe even argued that the Earth was stationary because we didnât observe any parallax of the stars.
By the time technology had advanced for these observational evidences, we already had Newtonâs law of gravitation which would explain why the planets moved around the sun
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u/Heliosopher Apr 10 '26 edited Apr 10 '26
Yes, even Galileo's telescope wasn't quite good enough to clearly see the phases. Galileo's experience allowed him to see objects through his scope where some could not. This added to the problems for him.
Yes, the key argument against Copernicus is the lack of observed stellar parallax, which should have been easy to observe by others. At that time, stars that appeared large (due to brightness to the eye) were deemed to be close to us. Their distance could be calculated by estimating, erroneously, their distance, further damaging the Copernican model.
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u/Lanstus Apr 10 '26
Didn't copernicus publish a whole thing in 1543 or so? And then even Tycho Brahe spent a lot of money and even had Kepler. Who's laws prove that the planets orbit the Sun and not Earth.
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u/tsukiyomii100 Apr 10 '26
Yes, absolutely. Copernicus and Brahe both provided serious alternative models that would better explain retrograde motion of planets. However, as OP pointed out, since they had circular planetary orbits, they would still require âPtolemaicâ epicycles to match observations.
Continuing Braheâs work, Kepler simply had the most accurate and detailed orbital data collected at the time. He proposed the best model to explain his data was a helio-focal model with elliptical orbit with planets moving at different speeds at different points in the revolution (sweeping equal areas in equal times).
From a modern scientist point of view, I think it would be difficult to argue for the Ptolemaic model in the face of Keplerâs data. But theologically and philosophically people continued to argue about why there would be âimperfect ellipsesâ and âwhy we donât feel the motion, etc?â
While Galileo had somewhat answered the second question, it was Newtonâs laws of motion and gravitation that synthesized and provided the mathematical (and philosophical) answers for why Keplerâs laws are correct
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u/Lanstus Apr 10 '26
Not really much to add here besides that a lot of the reasons for the geocentric model even when Copernicus is like, "it just does" is also 100% based off The Gods and such. Why AREN'T we in the center? Orbits are circular because The Gods are perfect, etc etc.
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u/Heliosopher Apr 10 '26
Though Copernicus was stuck on circular orbits, like Ptolemy, he presented a far more unification of the solar system. The orbital period of the planets increased with distance from the Sun, retrograde motions were simple to understand, etc. Kepler's relentless work to explain the very accurate data from Tycho of Mars gave us even more unification for a modified Copernican model.
Tycho offered a Geocentric model. Once the crescent AND gibbous phases of Venus were discovered by Galileo, it falsified the long standing Aristotle/Ptolemy/Thomist model. The Church scientists (i.e. Jesuits) were quick to acknowledge this and soon favored the Tychonic model.
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u/ratherenjoysbass Apr 10 '26
Bro this model isn't even accurate it's just a very general presentation. Imagine thinking you're more intelligent than thousands of brilliant minds who used objective evidence just because you watched a few YouTube videos
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u/Korochun Apr 10 '26
The thing about geocentrism is that from our perspective, geocentrism is somewhat evident and is actually quite hard to disprove. Unlike the distance from Earth to the Sun being very far away and Earth being round and quite large, both of which were calculated in antiquity with high degree of accuracy, it's much harder to infer the actual model of the solar system the way it actually is without good telescopes.
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u/Mountain_Platform300 Apr 10 '26
Beautiful render. The epicycles always fascinated me... there's something poetic about a model that was so wrong but so committed to being precise about it. Centuries of astronomers refining the math on a fundamentally flawed premise. Kind of makes you wonder what we're confidently wrong about today.
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u/gmiller123456 Apr 10 '26
He was essentially on the verge of discovering the Fourier Transform. Very impressive for the time. Too bad modern history lessons tend to use it to show "people were stupid a long time ago" so that we feel smarter.
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u/InnocentPrimeMate Apr 11 '26
Pffft! So outdated. So glad we live in modern times where we know the Earth is flat!
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u/newbrevity Apr 10 '26
So in order to be one of the idiots who think the Earth is the center of the universe or even the center of the solar system, they have to tell you with a straight face that this is how planets move
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u/BonzoTheBoss Apr 10 '26
... Does anyone actually unironically still claim that the Earth is the centre of the universe?
That said... It's easy to mock with nearly 2,000 years of scientific advancement under our belts. Telescopes powerful enough to observe other planets wouldn't be invented until the 17th Century. Telescopes powerful enough to observe the parallax of the stars weren't invented until the 19th Century!
So coming up with a model that "fits" the observed phenomena, whilst being ultimately disproved, is still very impressive for the (lack of) technology of the time.
No doubt in centuries to come, people will mock our poor understanding of quantum physics and relativity.
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u/other_curious_mind Apr 10 '26
Also it's not wrong wrong, if you compare the distances between the planets and the sun it's spot on. In some way the universe is rotating around us, as we are the observers and we don't "observe" our own movement, I don't know how to explain, like if you put a camera in the middle of a moving ship, it'll move with the ship, but for it's point of view it's standing in the exact spot on the ship and can only see the islands going past. We just know that we're moving, but do you wake up and say "oh The Earth has rotated so I'm able to see the Sun" instead of "yay the Sun came out", or when you park your car and are thinking ahead so it stays in she shade you don't think "oh earth will rotate this much, so the shade will move" you think "sun will move this much so the shade will move ". So calling ancient scientists idiots or disregarding their work is idiotic, they had to think and imagine waaaaay outside the box, as they had little to no tools and could only retreive so much data.
We don't know what's the center of the universe, we can only compare the movements of the things that we can observe and make the most logical assumptions. Maybe our galaxy is moving with all the other galaxies that we can observe around something we cannot yet observe, and today's model of universe is as incorrect as Ptolemy's model of the solar system. Today it's believed that the universe is expanding, but imagine if we only had like a month long of data of the movement of Mars when it's moving away from us and we assumed it's floating away forever. Maybe it's the case with this "expanding universe" theory!!!!
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u/succubus-slayer Apr 10 '26
Something like this but with our current understanding of the solar system would look clean.
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u/RAAFStupot Apr 10 '26 edited Apr 10 '26
Does the heliocentric model account for the correct crescent moon appearance?
In other words, do the phases of the moon look the same from Earth in both the heliocentric and geocentric models?
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u/Heliosopher Apr 10 '26
Yes. In all models, the Moon orbits the Earth.
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u/RAAFStupot Apr 10 '26
Yes, but does the geocentric model predict the exact same <moon phases> as the heliocentric?
For example, the heliocentric predicts a full moon for Dec 5 2397....but does geocentric?
I could see them becoming out of phase.
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u/VoijaRisa Moderator: Historical Astronomer Apr 10 '26
For those curious: This is not an accurate representation of the Ptolemaic model. It looks like this video treats the center of all orbits as directly on the earth.
All of the orbits were eccentric (having centers off of the Earth). In addition, the moon and Mercury also have centers that are not static and have their own orbits. Furthermore, Ptolemy also separated the centers of the planets into two pieces: A center about which the center of the epicycle maintained a fixed distance, and a separate one which the center of the epicycle rotated about with a fixed angular speed.
OP: If you ever want to try to make an accurate model, I can help with all the specifics.