The Celestial Spheres and the Ptolemaic and Copernican System
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The Celestial Spheres, The Ptolemaic and Copernican Cosmos Ron Shigeta PhD
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Describes the evolution of our conception of the heavens, from the Ptolemaic to the Copernican system
Transcript of The Celestial Spheres and the Ptolemaic and Copernican System
The Celestial Spheres, The Ptolemaic and Copernican
Cosmos
Ron Shigeta PhD
“Fact” #1 GeoCentrism
The most obvious truth about the heavens - the sun and planets spin about the earth every day.
“Fact” #2 Earth is uniquely flat
The planets, like the moon and sun are spherical, but are small, while the earth is vast and flat.
Aristotelean CosmologyFour elements,
Water, Earth, Air, and Fire.
Each with its own place
Each drawn to its respective place by a Natural motion, either up or down.
“Fact” 3: the heavens, like all things on the earth are supported by elements
Ptolemaic CosmologyStars, Moon and
Planets each have their own sphere.
Concentric spheres spinning moved by the motion of the outermost
Between each sphere, the fifth element the ether.
Then finally a fixed sphere of stars.
An perfectly ordered world?
The Obvious Becomes Complicated
A Fanciful Cosmos, though quite small
Copernicus Published: De revolutionibus orbium coelestium (1543)
Perfectly circular orbits, supported by ether spheres.
Sun is central.
The distance to the firmament (stars) is much greater than the distance to the sun.
Epicycles, equants, deferents still used because perfectly circular orbits were assumed (the true orbits are not perfect circles).
Galileo sees the Jovian Moons (1610)
