Order and Origin of the Greek Cosmos#
Second article based on my talk on «Greek Cosmogony and Cosmology» of astronomy in the Parque de los Deseos on May 14, 2013 (the first was Greek Cosmogony).
Thales of Miletus, the first Greek philosopher, incorporated the first non-mythological notions into the description and explanation of the world and tried to clarify the mystery of the first substance, considering it water. For Thales, the world was a circular disk floating in the ocean. Anaximander (the second Ionian philosopher) would abandon the views of Thales and the arche, and assign the infinite or the indefinite as the principle. By symmetry, the Earth should be flat or convex and in equilibrium with the center of the universe. The nature of the heavens is fire and it is spherical. The celestial bodies are located at different distances, with the sun being more distant than the sphere of fixed stars. The celestial bodies are holes that allow the fire of the sky to be seen.
Anaximenes (the third Ionian philosopher) found the principle in the air, which, by compression or rarefaction, would lead to the creation of everything. The Earth has its origin in dense air. The Earth, like the moon, the sun and the planets, is flat, and the fixed stars are like nails in a solid.
Xenophanes, the founder of the Eleatics, considered the principle in the Earth. The Earth is flat and embedded in infinity, while the sun, comets and stars are incandescent clouds. The sun and the stars are formed daily from clouds of burning particles, while the moon is a compressed cloud whose brightness comes from an inherent light that is extinguished monthly.
Parmenides, virtual founder of the Eleatics, is responsible for the first distinction of a spherical Earth. He considers the entire universe in concentric spherical layers around the stationary Earth. It is the first conception of concentric spheres. He considered the moon’s brightness to be a reflection of the sun’s light, and the origin of these was the residual material of the Milky Way. Like Anaximander, he makes the same mistake of placing the fixed stars closer than the sun. Heraclitus would consider fire a principle based on the fact that everything came to flow. The sun would be formed from exhalations from the Earth.
Anaxagoras affirms that the universe contains only two things: an infinite number of small particles (atoms) and the void that extends to infinity. Atoms are made of the same thing but differ in shape and size. It incorporates Leucippus” principle of causality. Democritus affirms that the shadows of the moon reflect the existence of mountains, losing the perfect nature of the moon. These constitute Greek atomism, and the three together support a flat Earth.
For the Stoics, the cosmos is finite and surrounded by an infinite void. It is in a state of flux, pulsating in size periodically. Aristotle proposed a spherical Earth surrounded by concentric celestial spheres between which the first ones around the Earth are the elements in the order earth, water, air and fire. The universe exists unchanged throughout eternity. It contains a fifth element called ether, above which the celestial bodies are found.
Aristarchus introduces the first mention of the sun in the center, in which, following the line of thought of Philolaus (the Pythagorean who proposes the first non-geocentric model with a central fire), he identified the central fire with the sun and assigned the correct positions to the planets. he Earth rotates and orbits the sun. The sphere of fixed stars is so distant that it is impossible to detect parallax.
To know more
The cosmological ideas among the Greeks. Hector MacPherson, Popular Astronomy, Vol. 24, p.358 (1916).
Evolution in the Greeks. Cosmoscalibur, May 13, 2012.
Arche. Wikipedia (english version). June 18, 2013.