Aristarchus of Samos: An Ancient Philosopher with Modern Ideas

Early calculations of the Sun, Moon, and Earth sizes.
Aristarchus's calculations on the relative sizes of the Sun, Earth, and Moon. These were done in the 3rd century B.C.E. Public Domain.

Much of what we know about the science of astronomy and celestial observations is based on observations and theories first proposed by ancient observers in Greece and what is now the Middle East. These astronomers were also accomplished mathematicians and observers. One of them was a deep thinker named Aristarchus of Samos.  He lived from about 310 B.C.E. through approximately 250 B.C.E. and his work is still honored today.

Although Aristarchus was occasionally written about by early scientists and philosophers, especially Archimedes (who was a mathematician, engineer, and astronomer), very little is known about his life. He was a student of Strato of Lampsacus, head of Aristotle's Lyceum. The Lyceum was a place of learning built before Aristotle's time but is most often connected to his teachings. It existed in both Athens and Alexandria. Aristotle's studies apparently did not take place in Athens, but rather during the time when Strato was head of the Lyceum at Alexandria. This was probably shortly after he took over in 287 B.C.E. Aristarchus came along as a young man to study under the best minds of his time.

What Aristarchus Achieved

Aristarchus is best known for two things: his belief that Earth orbits (revolves) around the Sun and his work attempting to determine the sizes and distances of the Sun and Moon relative to each other.

 He was one of the first to consider the Sun as a "central fire" just as the other stars were, and was an early proponent of the idea that stars were other "suns". 

Although Aristarchus wrote many volumes of commentary and analyses, his only surviving work, ​On the Dimensions and Distances of the Sun and Moon, does not provide any further insight into his heliocentric view of the universe.

While the method he describes in it for obtaining the sizes and distances of the Sun and Moon is basically correct, his final estimates were wrong. This was moore due to a lack of accurate instruments and an inadequate knowledge of mathematics than to the method he used to come up with his numbers.

Aristarchus's interest wasn't limited to our own planet. He suspected that, beyond the solar system, the stars were similar to the Sun. This idea, along with his work on the heliocentric model putting the Earth in rotation around the Sun, held for many centuries. Eventually, the ideas of later astronomer Claudius Ptolemy — that the cosmos essentially orbits Earth (also known as geocentrism) — came into vogue, and held sway until Nicolaus Copernicus brought back the heliocentric theory in his writings centuries later. 

It is said that Nicolaus Copernicus credited Aristarchus in his treatise, De revolutionibus caelestibus. In it he wrote, "Philolaus believed in the mobility of the earth, and some even say that Aristarchus of Samos was of that opinion." This line was crossed out prior to its publication, for reasons that are unknown. But clearly, Copernicus recognized that someone else had correctly deduced the correct position of the Sun and Earth in the cosmos.

He felt it was important enough to put into his work. Whether he crossed it out or someone else did is open to debate.

Aristarchus vs. Aristotle and Ptolemy

There is some evidence that Aristarchus's ideas were not respected by other philosophers of his time. Some advocated that he be tried before a set of judges for putting forth ideas against the natural order of things as they were understood at the time. Many of his ideas were directly in contradiction with the "accepted" wisdom of the philosopher  Aristotle and the Greek-Egyptian nobleman and astronomer Claudius Ptolemy. Those two philosophers held that Earth was the center of the universe, an idea we now know is wrong. 

Nothing in the surviving records of his life suggest that Aristarchus was censured for his contrary visions of how the cosmos worked.

However, so very little of his work exists today that historians are left with fragments of knowledge about him. Still, he was one of the first to try and mathematically determine distances in space. 

As with his birth and life, little is known of Aristarchus's death. A crater on the moon is named for him, in its center is a peak which is the brightest formation on the Moon. The crater itself is located on the edge of the Aristarchus Plateau, which is a volcanic region on the lunar surface. The crater was named in Aristarchus's honor by the 17th-century astronomer Giovanni Riccioli. 

Edited and expanded by Carolyn Collins Petersen