The geocentric theory The geocentric model was a postulate that defended the thesis that the Earth was the center of the universe. According to the theory, the Earth was immobile while the planets and the stars revolved around it in concentric spheres..
The philosopher Aristotle is credited with creating the geocentric theory which, as mentioned above, stated that the Earth was the central axis of the universe. This theory was upheld and expanded by Ptolemy, and later supplemented by the heliocentric theory of Copernicus..
Since its origins, man has faced doubt about existence. The rationality achieved by the human species has led it to create an infinite system of questions about its origin and that of the world that surrounds it..
As we evolved, the way of approaching the answers also did, giving way to a myriad of theories that prevailed at the time and that were repealed or replaced by new approaches..
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Cosmology is a science that has gone hand in hand with philosophy since time immemorial. The Greek, Egyptian and Babylonian philosophers, among others, found in the observation of the celestial vault a universe of possibilities; these possibilities refined and established the phases of the development of philosophical thought.
Platonic duality, which had a great influence on Aristotelian thought, supported the idea of the existence of two worlds: one formed by the four elements of nature (earth, air, fire, water) that is in subsistent movement (world sublunar), and another immobile, incorruptible and pure, known as the fifth essence (supralunar world).
The origin of the geocentric theory dates back approximately to the times when Plato argued that the Earth was located at the center of the universe and the planets and stars surrounded it, rotating in celestial circles..
His vision conformed to a mythical explanation of his thesis ("The myth of Er" in his book The Republic). In this he makes an analogy between his idea of the mechanics of the cosmos and the myth that refers to the "spindle of necessity", to explain how bodies revolved around the Earth.
Later, approximately in the year 485 a. C., highlighted a disciple of Plato called Eudoxo. He was born in the city of Knidos and was a mathematician, philosopher and astronomer.
Eudoxus had news about the studies carried out in Egypt related to astronomy and he prepared to be in contact with the observations and theories carried out so far by the priests.
In one of his books called Speeds explained the movement of the stars through a system of 4 spheres assigned to each one.
This canon of the solar system proposed that the Earth was spherical and was located in the center of the system, while around it three concentric spheres alternated.
These spheres were the following: an external one with a rotation that lasted 24 hours and carried the immobile stars, another in the middle that rotated from east to west and lasted 223 lunations, and an internal one that contained the Moon and rotated for 27 more days. five hours and five minutes.
To explain the movement of the 5 planets, 4 spheres were assigned to each one, while the Moon and the Sun required 3 spheres each..
Aristotelian cosmology was based on the philosophy of nature, which ran on the world that is perceived through the senses (corporeal) through a dialectic aimed at discovering the area in which the truth becomes tangible..
Aristotle optimized Eudoxus' proposal. The Aristotelian method proposed the planet Earth as the center of the universe, while the so-called celestial bodies alternated around it within spheres that rotated infinitely in a concentric way..
It is understandable that for the ancients the idea that the Earth occupied the very center of the universe was credible. Standing looking from the planet to the sky, they perceived that it was the universe that was moving around the Earth, which for them was an immobile, fixed point. The ground was the flat place from where the stars, the Sun and the Moon were observed.
The advancement of civilizations and centuries of study and knowledge allowed the ancient astronomers of Babylon and Egypt - and even contemporary Mediterranean ones - to forge the first idea about the shape of the Earth and its location at the center of the universe..
This notion continued until the seventeenth and eighteenth centuries, when new ideas emerged in pursuit of scientific evolution..
Those who joined this approach did so on the basis of observations. One of these was that, if the Earth was not immobile, then we could see the fixed stars move, a product of stellar parallax..
They also argued that, if so, the constellations would undergo significant changes in the period of one year..
The theory of concentric spheres initiated by Eudoxus and taken up by Aristotle was put aside as it had not been possible to develop an efficient and precise system based on this ideal..
Even so, the model proposed by Ptolemy - which was quite close to Aristotelian - was sufficiently ductile to fit the observations over many centuries..
The idea about the concentric spheres of Eudoxus did not explain the differences in the clarity that was perceived on the surface of the planets, caused by a variation in the distance.
The Ptolemaic system was founded on this, created by Claudius Ptolemy, an astronomer from Alexandria, in the 2nd century AD. C.
His work The almagest it was the result of the work carried out by Greek astronomers for centuries. In this work the astronomer explains his conception of planetary mechanics and the stars; It is considered the masterpiece of classical astronomy.
The Ptolemaic system is based on the idea of the existence of a great external sphere called the immobile motor, which is characterized by being an incorruptible essence or ether that motorizes the sensible world, remaining immobile and perfect..
This Ptolemaic model proposes the idea that each planet depends on the movement of two or more spheres: one corresponds to its deferent, the largest circle centered on the Earth; and the other corresponds to the epicycle, which is a smaller circle that moves along the vas rotating with a uniform motion.
The system also explained the lack of uniformity in the speed of the retrograde motion experienced by the planets. Ptolemy solved it by including the idea of the equant; an external point adjacent to the center of the Earth from which the planets were perceived to be moving at a constant speed.
So, it can be said that the idea of the epicycle, the deferent and the equant were Ptolemy's contributions to geocentric theory from a mathematical notion, which refined the ideas of the first hypotheses on the subject raised by Apollonius of Perga and Hipparchus of Nicea..
The Ptolemaic spheres were arranged starting from the Earth: the closest was the Moon followed by Mercury and Venus. Then there were the Sun, Mars, Jupiter and the most distant: Saturn and the static stars.
The West eventually accepted the resulting system, but Modernity found it complicated. However, the prediction of different celestial movements - including the end and the beginning of the retrograde movements - was a very acceptable achievement for the time in which it arose..
- Earth is the center of the universe.
- There is no void in the universe and it is finite.
- Each planet moves within 4 concentric and transparent spheres, and the Sun and the Moon move within 3 spheres, each.
- There are two worlds: the corporeal or the sensible, which is corruptible and in constant motion; and the other world, perfect, pure, static and incorruptible, which is the essence of all movement in its environment.
- The term equant is used, which corresponds to the point that standardizes the astral and planetary movement with respect to the Earth..
- The term epicycle also arises, which is the circular path of the planets.
- Another characteristic notion is the deferent, which is the outermost circle of the Earth on which the epicycle moves and rotates..
- Mercury and Venus are the inner planets and their movements were established to ensure that the lines with respect to the deferent were always parallel from the equating points.
Within the abundant information on this subject, one of the theses that gained more force in Modernity was that the heliocentric theory promulgated by Copernicus arose to perfect the Aristotelian and Ptolemaic system, not to replace it.
The objective was that the calculations were more exact, for which he proposed that the Earth be part of the planets and the Sun be considered the center of the universe, keeping the circular and perfect orbits intact, as well as the deferents and epicycles..
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