Aristotle: philosophy and round Earth

Aristotle: philosophy and round Earth

Aristotle (384-322 B.C.) was a Greek philosopher and scientist who is considered, along with Plato and Socrates, as one of the most prominent thinkers of ancient Greek philosophy and possibly the most influential in the whole of all Western philosophy.

He was born in Estagira (current Greek city of Stavro, then belonging to Macedonia), which is why he was also later known by the nickname of El Estagirita. Son of a doctor of the royal court, he moved to Athens at age 17 to study at Plato's Academy. He remained in this city for approximately 20 years, first as a student and, later, as a teacher. After Plato died (c. 347 B.C.), Aristotle moved to Assos, a city in Asia Minor where his friend Hermias de Atarnea ruled.

After being captured and executed Hermias by the Persians (345 BC), Aristotle moved to Pela, former capital of Macedonia, where he became guardian of Alexander (later Alexander III the Great), youngest son of King Philip II.

In 336 B.C., when Alexander entered the throne, he returned to Athens and established his own school: the Lyceum. Because much of the discussions and debates took place while teachers and students walked along their covered walk, their students were called peripatetics.

The death of Alexander (323 BC) in Athens generated a strong feeling against the Macedonians, so Aristotle retired to a family property located in Calcis, on the island of Euboea, where he died a year later.

He was one of the most important Greek philosophers and scientists. His influence was such that some of the theories he developed are still valid, two thousand years after his death.

In the astronomical field, he advanced the first solid arguments against the traditional theory of the flat Earth, noting that the stars seem to change their height on the horizon according to the position of the observer on Earth. This phenomenon can be explained based on the premise that the Earth is a sphere; but it is incomprehensible assuming it is flat.

Aristotle also noted that during lunar eclipses, when the Earth's shadow is cast over the Moon, the shadow cone line is curved. He also developed a model of the Universe that was based on the geocentric system proposed by Eudoxo of Cnido (Eudoxium) and successively modified by Calipo.

In the Eudoxium system, called of the homocentric spheres (which have a common center), the Earth was imagined motionless in the center of the Universe and the celestial bodies then known, fixed to seven groups of spheres of increasing dimensions from the innermost to the outermost: three spheres belonged to the Moon, three to the Sun and four to each of the planets then known (Mercury, Venus, Mars, Jupiter and Saturn), with a total of 26 celestial spheres.

Later Calipo, disciple of Eudoxio, in order to make the whole set work better, brought the total number of spheres to 33. However, it seems that Eudoxio and Calipo thought of their spheres as a geometric resource, lacking physical consistency, invented only to explain and anticipate the movement of celestial bodies.

On the other hand, Aristotle considers that the spheres, constituted by a pure and transparent substance, actually surrounded the Earth, having all visible celestial bodies enshrined as diamonds.

In an attempt to explain the origin of planetary movements, Aristotle thought of a "divine force" that transmitted his movements to all spheres from the outermost, or sphere of fixed stars, to the innermost, or sphere of the Moon . However, this idea translated into a huge complication of the entire system, since it raised the total number of spheres from 33 to 55, all related to each other.

The theory described in his work "Metaphysics" was replaced by the system of Ptolemy (2nd century), always geocentric, but which more accurately took into account the celestial movements and was universally accepted until Copernicus. Among the scientific works of the Greek philosopher dedicated to heaven, it is necessary to remember the "Metereology" and the "De Coelo".

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Eudoxo of Cnido and the spheresEuclid, the father of geometry