Theory of the movement of celestial bodies

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Theory of the movement of celestial bodies

• Example of multiple theories explaining the same
  data
• Terra centric (Ptolemy)
• Assertion that earth is the center of planetary
  movements
• Planets orbit the earth
• Planets have additional orbits (not around
  another heavenly body)
• Helio centric (Copernicus)
• Assertion that sun is the center of planetary
  movements
• Planets orbit the sun
• Earth orbits the sun like other planets

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• Assumptions
• Planets move in the sky in relationship to the
  center
• Planets are in different positions in
  relationship to center
• Predictions
• Planets will move in certain patterns (as
  observed)
• These theories were developed based on
  astronomical observations
• Built to explain the observations

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Ptolemyan terra centric theory

• Observational pattern
• Planets move across the sky
• Forward movements sometimes reverse
• Explain by modeling dual orbits

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Copernican helio centric theory

• Since both the earth and other planets orbit the
  sun
• From the point of view of the earth the orbits of
  the other planets appear to back track

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Which theory is right?

• They are both right
• It depends on the perspective
• But the Copernican is more elegant
• It can explain the complex pattern with fewer
  parameters
• No need for the extra orbit