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c. 360 BCE – Eudoxus of Cnidus proposes for first time a purely geometric-mathematical, geocentric model of the planetary movements, including that of the Sun and the Moon. [19] c. 350 BCE – Aristotle argues for a spherical Earth using lunar eclipses [20] and other observations.
The cosmological model of concentric (or homocentric) spheres, developed by Eudoxus, Callippus, and Aristotle, employed celestial spheres all centered on the Earth. [1] [2] In this respect, it differed from the epicyclic and eccentric models with multiple centers, which were used by Ptolemy and other mathematical astronomers until the time of Copernicus.
Eudoxus emphasised that this is a purely mathematical construct of the model in the sense that the spheres of each celestial body do not exist, it just shows the possible positions of the bodies. [23] His model was later refined and expanded by Callippus. Geocentric celestial spheres; Peter Apian's Cosmographia (Antwerp, 1539)
In Aristotle's fully developed celestial model, the spherical Earth is at the centre of the universe and the planets are moved by either 47 or 55 interconnected spheres that form a unified planetary system, [19] whereas in the models of Eudoxus and Callippus each planet's individual set of spheres were not connected to those of the next planet ...
The two innermost homocentric spheres of his model are represented as rings here, each turning with the same period but in opposite directions, moving the planet along a figure-eight, or hippopede The basic elements of Ptolemaic astronomy, showing a planet on an epicycle (smaller dashed circle), a deferent (larger dashed circle), the eccentric ...
Eudoxus, son of Aeschines, was born and died in Cnidus (also transliterated Knidos), a city on the southwest coast of Anatolia. [3] The years of Eudoxus' birth and death are not fully known but Diogenes Laërtius gave several biographical details, mentioned that Apollodorus said he reached his acme in the 103rd Olympiad (368– 365 BC), and claimed he died in his 53rd year.
This understanding was accompanied by models of the Universe that depicted the Sun, Moon, stars, and naked eye planets circling the spherical Earth, including the noteworthy models of Aristotle (see Aristotelian physics) and Ptolemy. [8] This geocentric model was the dominant model from the 4th century BC until the 17th century AD.
Eudoxus, a student of Plato, was born around 400 BC. [4] A mathematician and an astronomer, he generated one of the earliest sphere-centric models of the planet systems, based on his background as a mathematician. Eudoxus's model was geocentric, with the Earth being a stationary sphere at the center of the system, surrounded by 27 rotating ...