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For introduce us to Greek cosmology, the first thing we must do is understand its meaning and differentiate it from the cosmogony.
Difference between cosmology and cosmogony
The cosmogony on the one hand it is a science that deals with explain how the universe was formed using myths about gods.
A clear example is found in the work ‘Theogony’ by Hesiod.
Instead, cosmology tries to explain the creation of the universe in a rational way, with proven physical laws, and that are those that govern the universe.
Cosmology as such was born in Greece, and its base of study begins with the cosmological bases of the Egyptian and Babylonian cultures.
Greek astronomers and philosophers and cosmology
Next, they are exposed to the most prominent philosophers of Greece, who tried to give as exact a theory as possible of how the universe worked.
Pythagoras of Samos (496 BC)
Among the most prominent theories of the proposed model are that the Earth has a spherical shape, that it is not in the center of the universe, and that it also moves (Geocentric Theory).
Thales of Miletus (624 BC - 546 BC)
This Greek philosopher dedicated his life to the study of the stars. Among his most surprising discoveries are that deduced that the moonlight was due to the reflection of the sun.
He also provided calculations on the number of days in a year, and was also able to explain the origin of lunar and solar eclipses.
Anaximander (610 BC - 545 BC)
Thanks to the observation of the stars, Anaximander of Miletus was the first character in history who tried to give his explanation of how the world worked without resorting to myths, arguing with science.
This philosopher established that the earth floated in the middle of the cosmos, in addition to making the first maps.
He also stated in his theory that the first living things were formed in water, and from there we humans arose, a theory not too distant from what is known today.
Plato (427 BC - 347 BC)
One of the first Greek philosophers to propose an idea of how the universe was formed was Plato, although he did so by giving an explanation based on mythology, in the Timaeus.
Plato stated that Demiurge was the creator of the universe in the midst of chaos, and that it consisted of 4 elements: air, fire, earth and water.
Thus he established that the universe should be spherical in shape, and the bodies within it move in a circular fashion, as it is perfect.
In addition, it established a geocentric model with Earth suspended in the middle of the celestial sphere.
Eudoxus of Knidos (408 BC - 355 BC)
The cosmological model that Eudoxus proposes is based on 27 spheres, in which, the Earth remained static in the center of the Universe, while 3 concentric spheres rotated around them, with planets on their axes.
Back then only 5 planets were known, to which he assigned 4 spheres rotating around each one, while for the Sun and the Moon he assigned 3 spheres rotating each one.
Aristotle (384 BC - 322 BC)
In broad strokes of his cosmological idea of the universe, it can be extracted that the Earth is spherical and does not move, but the sky and the rest of the universe are those that revolve around it.
It can also be said, that he believed that the universe was finite, and was composed of several concentric spheres, where the Earth was located in the center of everything.
Aristarchus of Samos (310 BC - 230 BC)
Aristarchus was one of the most important scholars of the greek cosmology. He was one of the first astronomers to propose a model of the heliocentric cosmos. In other words, the Sun is the center of our universe.
Also, proposed that the moon revolved around the Earth, and that the radius of our satellite was half the radius of the Earth. This could be measured thanks to experiments done in an eclipse.
Not only these contributions will make Aristarchus, too determined distances from the Earth to the Moon and from the Earth to the Sun. Within the philosophers and astronomers of ancient Greece, was the one that was closest to the contemporary model known from the universe.
Eratosthenes (276 BC - 194 BC)
His greatest achievement in astronomy was the fact that closely approximate the actual size of the EarthAccording to his calculations, it failed by only 567 kilometers.
He is also credited with other important discoveries such as the precursor of the Julian calendar (which says that every 4 years there is one more day) and he was able to measure degree of inclination of the planet, in this case being imprecise, a situation that perfected Hipparchus.
Apollonius of Perge (262 BC - 190 BC)
This character from ancient Greece was the one who introduced the parable and hyperbola in the planetary system.
Hipparchus of Nicaea (190 BC - 120 BC)
It is considered the greatest astronomer of the ancient era. He achieved facts such as measuring the distance between the Earth and the Moon, and the Earth and the Sun.
Also, refuted Aristotle's theory, which said that the stars were fixed.
This astronomer was in charge of discover the precession of the equinoxes. This discovery is credited to him as one of the most important of his life.
Also, he is considered the inventor of trigonometry.
Claudius Ptolemy (100 - 170 AD)
This astronomer assumes that the Earth is the center of our universe, and that all celestial bodies revolve around it. It is known as «Geocentric Theory«.
Conclusion of Greek cosmology
As we have been able to appreciate, in ancient Greece almost all philosophers, mathematicians, astronomers and scientists, believed that the universe system was geocentricHowever, only one of these, Aristarchus, proposed a much more real model than the current one, with the heliocentric theory (the sun is the center).
Thus we conclude a passage through the beginnings of Greek cosmology, describing the scientists and astronomers who in one way or another tried to explain the behavior of the stars, through their imagination and based on scientific facts, thus completely reviewing the most significant contributions of each one of them.
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