Sunday, January 23, 2011

The Ptolemaic System

The Ptolemaic System

This system was used to explain the motions of the heavens. 
This cosmological model was espoused by Claudius Ptolemaeus around the 2nd century C.E.

Unlike earlier systems (i.e., the stars move because it is the will of the 'gods'), the Ptolemaic model explained all the phenomena i the sky while holding to Plato's dictum, which states that all motions in the heavens can be explained with uniform circular motion and obeying Aristotelian physics.

According to the Ptolemaic model:

  • Earth is at the center of the universe
  • Heavenly bodies are attached to crystal spheres
  • Moon was the innermost sphere and touched the Earth realm

Problems with Ptolemaic system:
  • Size of a planet's retrograde loop (most notably mars) would be smaller, and sometimes larger.
Galileo disproved Ptolemy's model, when, using his telescope, he discovered that Venus goes through phases.
Under the Ptolemaic system, Venus could not undergo all those phase changes. The only reasonable explanation would be for Venus to orbit the sun.

1 comment:

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