From the Antiquity the man observed that stars in the sky existed that, with the passage of the days, described irregular trajectories. These trajectories were made with a variable speed. In the sixth century, these bodies the Greek philosopher Anaximenes called Planets, to differentiate them from the stars.
The first theories about the movement were made by another Greek mathematician, philosopher and astronomer, Eudoxio, in the 5th century BC. They consisted of concentric crystalline spheres that with their regular movements represented the movements of the planets. To reproduce the movements of the Sun, I needed three spheres, as for the Moon; for the known planets then used four, forming a total of 27 spheres.
Following in Ancient Greece, the philosopher Aristotle was responsible for modifying the Eudoxio system. He turned it into a compact mechanical model that used 55 spheres to represent planetary movements. In both the Eudoxio and Aristotle models, the Earth occupied the center of the known universe.
Aristarchus and Hipparchus
It was the Greek astronomer Aristarchus of Samos who first formulated a heliocentric theory. His treatise was based on the hypothesis that both the stars and the sun remained motionless, while the earth revolved around the sun according to a circle, the sun being the center of that orbit.
The contributions of Hipparchus of Nicea have been transcendental for Astronomy, and especially for celestial mechanics. To him is due the first catalog that was made of the stars; the division of the day into 24 hours of equal duration; the discovery of the equinoxes; distinguished between sidereal year and tropic year; He set the distance between Earth and the Moon more accurately and was the inventor of trigonometry and the concepts of geographical longitude and latitude.
In Roman times
Already in the early days of the Roman Empire, the Greco-Egyptian astronomer Ptolemy made a review of some of the theories of Hipparchus, but based on geocentric theory. Despite this he did a magnificent empirical work studying a large amount of existing data on the movement of the planets.
He built a geometric model with them that explained their positions in the past and was able to predict their future positions. His most important legacy was the Almagesto, which remains the most prominent book in predictive geometric astronomy. Explain the movements of the planets within a geocentric system, in which the Sun, Moon and planets revolve around the Earth in circles epicyclic (circles whose centers, in turn, move in circles; too complicated to be true).
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