Why Was Aristarchos’s Heliocentric Model Dismissed and Ignored?

Many people are astonished to learn that the concept of heliocentrism did not originate with Nicolaus Copernicus, but rather with the ancient Greek astronomer Aristarchos of Samos (lived c. 310 – c. 230 BC), who published a book in around the early third century BC in which he argued that the Earth orbits around the Sun. This book has not survived, but we know about its existence because it is referenced by later authors.

What shocks many people even more than the fact that Aristarchos came up with the idea of heliocentrism in the third century BC is the fact that Aristarchos’s heliocentric model of the universe was almost totally rejected by ancient Greek and Roman scholars and never caught on in antiquity. Many people wonder why it was that the ancient Greeks never took Aristarchos seriously. In order to find out why Aristarchos’s heliocentric model of the universe was rejected, we are going to need to dive deep into the ancient sources.

Non-geocentric views before Aristarchos

As I discuss in this article I published in February 2019, it has been continuous common knowledge in the western world ever since the late fifth century BC that the Earth is a sphere. People before Aristarchos knew perfectly well that the Earth is a sphere. Nonetheless, no one before Aristarchos is known to have argued that the Earth orbits around the Sun.

Aristarchos of Samos is the first person who is recorded to have proposed a fully heliocentric model of the universe, but there were other people before him who proposed non-geocentric models of the universe. Notably, a view that seems to have been prevalent among Pythagoreans in the fifth and fourth centuries BC held that the center of the universe was something known as “the central fire” and that all the celestial bodies—including both the Earth and the Sun—orbited around this central fire.

The Pythagoreans who believed in this view thought that the central fire was invisible to all people on their side of the Earth because the Earth orbited the central fire with one side always facing it and the other side always facing away and they believed that they lived on the side that was always facing away. They believed that the Sun was a mirror that reflected the light and heat from the central fire onto the Earth. They referred to the central fire as the “Διὸς πύργος” (Diòs pýrgos), which means “the Watchtower of Zeus.” They also called it the “ἑστία τοῦ παντός (hestía toû pantós), which means “the Hearth of Everything.”

ABOVE: Diagram from Wikimedia Commons illustrating the Pythagorean model of the universe. The upper illustration shows how supporters of the system thought the system looked at night and the lower illustration shows how they thought it looked during the day.

The Pythagoreans who believed in this cosmological model also believed that there was another planet known as “Ἀντίχθων” (Antíchthōn), or “Counter-Earth,” that was also orbiting the central fire. They believed that this planet was the same size and shape as the Earth and orbiting the central fire at exactly the same speed, but, because it was always on exactly the opposite side of the central fire from the Earth, it was always invisible. The Pythagoreans strongly believed in the importance of balance and symmetry, so they believed that this invisible “Counter-Earth” was necessary as the Earth’s cosmological counterpart.

This rather eccentric non-geocentric model of the universe is most closely associated with the Pythagorean philosopher Philolaos of Kroton (lived c. 470 – c. 385 BC). As I note in this article I wrote back in March 2018, the ancient Pythagoreans were more mystics than scientists as we think of them today and they believed most of the things they did not because they had evidence, but rather on the basis of mystical teachings. Many of the mystical teachings that the ancient Pythagoreans believed in seem bizarre and even, in some cases, absurd to most people today in the twenty-first century.

Philolaos and other Pythagoreans seem to have believed that the “central fire” was the center of the universe because they thought that fire was the noblest of all the elements and that it therefore must occupy the most central place in the universe. In other words, Pythagorean non-geocentric cosmological system was primarily rooted in mystical beliefs about the nature of the elements rather than in science and observation.

ABOVE: Woodcut from Franchino Gaffurio’s Theoria musice, published in 1492, depicting fictional representations of Pythagoras and Philolaos anachronistically playing music together. (In historical reality, no one knows what either of these men looked like and Philolaos was actually born about a generation after Pythagoras died.)

Archimedes on Aristarchos

None of Aristarchos’s own writings have survived to the present day. Furthermore, because Aristarchos’s ideas about the cosmos were generally not taken very seriously, his ideas are rarely ever discussed in extant writings. As a result of this, we know very little about what Aristarchos himself thought. Nonetheless, we can glean some very basic information about Aristarchos’s ideas from a small number of other ancient writers who mention him.

The ancient Greek mathematician and inventor Archimedes of Syracuse (lived c. 287 – c. 212 BC) evidently took Aristarchos of Samos seriously enough to cite him as a source and discuss his ideas about the universe in his treatise The Sand-Reckoner. Archimedes writes near the beginning of the treatise, as translated by Thomas L. Heath:

“But Aristarchus of Samos brought out a book consisting of some hypotheses, in which the premisses lead to the result that the universe is many times greater than that now so called. His hypotheses are that the fixed stars and the sun remain unmoved, that the earth revolves about the sun in 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. Now it is easy to see that this is impossible; for, since the centre of the sphere has no magnitude, we cannot conceive it to bear any ratio whatever to the surface of the sphere. We must however take Aristarchus to mean this: since we conceive the earth to be, as it were, the centre of the universe, the ratio which the earth bears to what we describe as the ‘universe’ is the same as the ratio which the sphere containing the circle in which he supposes the earth to revolve bears to the sphere of the fixed stars. For he adapts the proofs of his results to a hypothesis of this kind, and in particular he appears to suppose the magnitude of the sphere in which he represents the earth as moving to be equal to what we call the ‘universe.’”

This is the most detailed description we have of Aristarchos’s heliocentric model in any extant work. Unfortunately, Archimedes tells us nothing about why Aristarchos hypothesized that the Sun was the center of the universe. It is possible that Aristarchos proposed heliocentrism based on some kind of empirical evidence, but it is equally possible that Aristarchos’s heliocentric model of the universe was merely rooted in the same sort of mystical beliefs that gave rise to the Pythagorean view of all the celestial bodies orbiting around the central fire.

It is therefore difficult for us to judge whether Aristarchos of Samos was really a groundbreaking scientific thinker millennia ahead of his time as he often portrayed in popular writings or simply a mystic convinced of the elemental primacy of fire who just happened to be right about the Earth orbiting the Sun by accident. It is also possible that Aristarchos may have been some combination of both these things.

ABOVE: Diagram from a tenth-century AD Byzantine manuscript illustrating Aristarchos’s calculations of the relative sizes of the Sun, Earth, and Moon, as described by Archimedes in The Sand-Reckoner

Later in the same treatise, Archimedes cites Aristarchos again for his calculation of the size of the Sun. Archimedes writes, as translated by Heath:

“It is true that, of the earlier astronomers, Eudoxus declared it to be about nine times as great, and Pheidias my father twelve times, while Aristarchus tried to prove that the diameter of the sun is greater than 18 times but less than 20 times the diameter of the moon. But I go even further than Aristarchus, in order that the truth of my proposition may be established beyond dispute, and I suppose the diameter of the sun to be about 30 times that of the moon and not greater.”

One of the most common objections against the idea that the Earth might move in antiquity was the problem of parallax. Ancient astronomers observed that the same stars rise and fall in the night sky every year and, although they change position in the sky, they are always seen in the same formations. Ancient astronomers argued that, if the Earth were moving, then the stars would seem to change their formations in the sky as the Earth passed them.

Today, we know that the real reason why the stars seem to keep their formations is because they are so impossibly far away that parallax does not affect them. Although Archimedes does not explicitly say this, it is possible that Aristarchos’s extremely large estimates for the sizes of the Sun and the universe were meant to refute the objection from parallax.

ABOVE: Fictional (and anachronistic!) portrayal of Archimedes of Syracuse painted in around 1620 by the Italian Baroque painter Domenico Fetti. Much of what we know about Aristarchos of Samos comes from Archimedes’s treatise The Sand-Reckoner.

Ploutarchos on Aristarchos and his followers

Archimedes is not the only ancient author who wrote about Aristarchos’s heliocentric model in an extant work. The Greek biographer and Middle Platonist philosopher Ploutarchos of Chaironeia (lived c. 46 – c. 120 AD) also mentions Aristarchos’s heliocentric model of the universe in his treatise On the Face which Appears on the Surface of the Moon. Ploutarchos writes, as translated by Harold Cherniss and William C. Helmbold:

“Thereupon Lucius laughed and said: ‘Oh, sir, just don’t bring suit against us for impiety as Cleanthes thought that the Greeks ought to lay an action for impiety against Aristarchus the Samian on the ground that he was disturbing the hearth of the universe because he sought to save (the) phenomena by assuming that the heaven is at rest while the earth is revolving along the ecliptic and at the same time is rotating about its own axis.’”

You will notice that Ploutarchos here explicitly mentions the Pythagorean idea of the central fire in association with Aristarchos. He says that Aristarchos was accused of impiety for claiming that the Earth orbited the Sun rather than the central fire.

Ploutarchos mentions Aristarchos’s heliocentric model of the universe again in his Platonic Questions 8.1. In this passage, Ploutarchos states that Aristarchos only proposed heliocentrism as a hypothesis, but that his later follower Seleukos of Seleukia (lived c. 190 – c. 150 BC) went even further and asserted heliocentrism as a fact. Ploutarchos writes, as rendered in the translation edited by William W. Goodwin:

“Does the earth move like the sun, moon, and five planets, which for their motions he calls organs or instruments of time? Or is the earth fixed to the axis of the universe; yet not so built as to remain immovable, but to turn and wheel about, as Aristarchus and Seleucus have shown since; Aristarchus only supposing it, Seleucus positively asserting it? Theophrastus writes how that Plato, when he grew old, repented him that he had placed the earth in the middle of the universe, which was not its place.”

Unfortunately, Ploutarchos says nothing at all about what led Seleukos to definitively conclude that the Earth orbited around the Sun. We can perhaps guess that maybe Seleukos had some kind of evidence for heliocentrism beyond whatever Aristarchos had. Ultimately, though, we will probably never know what kind of evidence Seleukos had or how convincing that evidence might have been, because nothing has survived of Seleukos’s writings and the surviving authors tell us nothing more about his ideas on heliocentrism. Evidently, ancient Greek scholars did not find Seleukos’s arguments for heliocentrism very persuasive.

ABOVE: Modern conventional portrait of Ploutarchos from his hometown of Chaironeia, based on an ancient bust that was long thought to represent Ploutarchos but is now generally agreed to probably not depict him at all.

Why Aristarchos was not taken seriously

Although Aristarchos of Samos is mentioned by a few other ancient writers aside from Archimedes and Ploutarchos, none of those other ancient writers tell us anything more about Aristarchos’s hypotheses about the Earth possibly orbiting the Sun. As far as we can tell from the extant sources, Aristarchos’s model of full heliocentrism does not seem to have really caught on in the Greek world.

The main reason why Aristarchos’s hypothesis never caught on is probably because, whatever evidence Aristarchos had, scholars and astronomers apparently did not find it convincing. Unfortunately, since we do not know what evidence he had (if he had any evidence at all), it is difficult to assess why people did not find it convincing. It is entirely possible that Aristarchos simply proposed heliocentrism on the basis of mystical reasoning and not on the basis of any kind of empirical or mathematical evidence.

On the other hand, we should not assume that Aristarchos did not have any evidence to support his hypothesis. After all, we know that Aristarchos was proposing something very similar to what Copernicus proposed around eighteen centuries later and many scholars in Copernicus’s own time did not take what he was arguing seriously, even though he had mathematical models to back him up.

A secondary reason why Aristarchos’s hypothesis was never accepted is because it went against what educated people at the time thought they knew about physics. I have already mentioned the objection from parallax, which is generally considered to have been the strongest objection against heliocentrism. Indeed, the objection from parallax was still being brought up until stellar parallax was finally observed in the early nineteenth century, definitively proving that the Earth is moving.

Other objections against heliocentrism were rooted in Aristotelian ideas about motion. For instance, another objection that was made against non-geocentric conceptions of the universe was that, since heavy objects fall downwards towards the center of the Earth, the center of the Earth must be the lowest point in the universe. Another objection was that, if the Earth was turning, then the winds should be continually blowing strongly from the east. Since this was not the case, it seemed to many people that the Earth must not be turning.

ABOVE: Diagram from Wikimedia Commons illustrating the phenomenon of stellar parallax. One common objection against heliocentrism was the stellar parallax had never been observed, which, in many people’s mind’s meant that the Earth could not be moving. Today we know stellar parallax is real, but it is so slight that it is barely observable.

Partial heliocentrism

The writer Martianus Capella (floruit early fifth century AD), a pagan from North Africa who wrote in Latin, did not endorse full heliocentrism like Aristarchos of Samos or Seleukos of Seleukia, but he did endorse partial heliocentrism. Martianus Capella argued in Book Eight of his encyclopedic work On the Marriage of Philology and Mercury, written partially in prose and partially in verse, that the planets Mercury and Venus orbited the Sun. Nevertheless, he maintained that all the other celestial bodies, including the Sun, orbited the Earth.

To many modern readers, Martianus Capella’s system sounds like a bizarre hybrid of heliocentrism and geocentrism, but it was actually rooted in the astronomical knowledge that was available to him at the time. It explained the unusual motions of the planets Mercury and Venus while still maintaining the Earth as the center of the universe.

Unlike Aristarchos’s heliocentric model of the universe, Martianus Capella’s partially heliocentric model actually continued to be debated and discussed during the Middle Ages and during the Renaissance. We even still have Martianus Capella’s own writings; whereas, with Aristarchos, we only have a handful of references to him by later writers.

ABOVE: Illustration from 1573 by Valentin Naboth showing a diagram of Martianus Capella’s model of the universe. Martianus believed that the planets Mercury and Venus orbited the Sun, while the Sun, the Moon, and all other celestial bodies orbited the Earth.

Copernicus and Aristarchos

One thing that is very interesting is the fact that the Polish astronomer Nicolaus Copernicus (lived 1473 – 1543), whom we usually think of as having revived heliocentrism during the Renaissance, actually never mentions Aristarchos anywhere in the published version of his treatise On the Revolutions of the Heavenly Spheres. Instead, he cites the Pythagoreans who believed that the Earth orbited around the central fire and Martianus Capella as his inspirations.

We know that Copernicus knew about Aristarchos because he references him in an early unpublished draft of On the Revolutions of the Heavenly Spheres and yet, for some reason, he chose not to mention him in the final, published version of his treatise—even though Aristarchos’s heliocentric model of the universe is certainly much closer to Copernicus’s model than any of the models Copernicus actually cites in his treatise.

On the one hand, it is possible that Copernicus actually did not know that Aristarchos had proposed a heliocentric model of the universe, since the only point where he cites Aristarchos in his unpublished draft of On the Revolutions of the Heavenly Spheres is in the context of a discussion of the respective sizes of the Earth, the Sun, and the Moon.

On the other hand, it is possible that the reason why Copernicus avoided citing Aristarchos may be because Copernicus wanted to portray himself as a modern-day Pythagorean reviving the lost teachings of an esoteric ancient sect. Since Aristarchos was not a Pythagorean and we have no definitive record of him as a mystic, Copernicus may have wanted to distance himself from him.

ABOVE: Portrait of a man from c. 1580, traditionally thought to be Nicolaus Copernicus, who is the man we usually think of as having revived heliocentrism during the Renaissance

Conclusion

Unfortunately, we do not know what evidence Aristarchos had to support his hypothesis that the Earth orbits the Sun. It is possible that he did not have any empirical evidence and simply proposed this idea based solely on mystical ideas about the element of fire derived from the Pythagoreans. In any case, whatever evidence he had was deemed unconvincing and his ideas went against ideas about physics that were seen as commonsensical at the time.

While the fully heliocentric model of Aristarchos was dismissed and ignored, other models that were not fully geocentric continued to be debated and discussed, such as the model of Martianus Capella. Ironically, it is entirely possible that Nicolaus Copernicus may not have known that Aristarchos had proposed heliocentrism around 1,800 years before his own time because the only time he references Aristarchos in the unpublished draft of his On the Revolutions of Heavenly Spheres is in a discussion about the sizes of the celestial bodies.