The War of the Centrics

1
The War of the Centrics!

• Topics
• Geocentric vs. Heliocentric
• Origins
• The THREE CONUNDRUMS of the Solar System.

2
Whats the difference between the Centrics?????

• Heliocentric Geocentric
• Which one is right? How do you know???

3
Modern science starts with the Greeks

• Based most of their thinking on observation and
  reason.
• The universe beyond Earth was perfect, beautiful,
  and unchanging!
• Geometry was the math of the day.
• Circles were considered the perfect shape!

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Pythagoras (569-475 BC)

• Geometry! a2 b2 c2
• Earth is a spherewhich is a perfect figure!
• Planetary motion is governed by geometric laws.
• Geometry begets HARMONY!

5
PLATO (428-348 BC)

• According to Plato, each of these 5 elements
  occupied a unique place in the heavens!

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Platos Universe

• This was the beginning of the Periodic Table!
• Heavy stuff was located closer to Earth.
• Lighter stuff occupied space at higher locations.

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Aristotle (384-322 BC)

• His model is based on Platos five solids and his
  own ideas on motionharmony, a natural state of
  rest, blah, blah.
• Aristotles model of the universe is called
  CRYSTALLINE SPHERES.
• Two moving spheresone holding the planetsthe
  other holding the starsEarth in the middle.
• All motion is circular with constant
  speednothing ever changes!

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SPHERESHMERE

• Why isnt the Earth flat in these early
  models?????
• Who is Eratosthenes (276-194 BC)???
• Why is the Earth at the center of the
  Plato-Aristotelian models?

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ARISTARCHUS (270 BC)

• Measured the size of the Sun.
• First to propose a Heliocentric Model of the
  Universe.

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Back to the drawing board

• Aristarchus model went south and Aristotles
  was back in action. But, there were problems.
  Ahhhhthe CONUNDRUMS!
• Retrograde Motion
• 2. Varying Speed of Planets

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Retrograde Motion

• Planets seem to change direction!
• Whats THAT all about?????

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The other one

• The planets seemed to move faster at different
  times. How could this be if everything in the
  universe moved with CONSTANT circular motion???
• Could it be that Aristotles
• reign is coming to an end???

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EnterPtolemy (120 AD)

• Geocentric Model!
• Used epicycles to explain retrograde motion.
• Maintained circular motion!
• Published book Algamest

Retrograde Animation
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What about that changing speed thing???

• The Equant

• Ptolemy moved the Earth off-center! Now the
  epicycles moved relative to an imaginary point
  called the EQUANT!
• Does this explanation violate uniform celestial
  motion?

Silence is Golden
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Things get too complicated

• Ptolemy got some mileage out of his model it
  dominated for over a millennium! But, as new
  data rolled in, it made less sense. And it was
  frequently tweaked, which made it very
  complicated!

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Copernicus (1473-1543 )

• Heliocentric Model!
• Maintained circular motion!

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Copernicus vs. Conundrums
Compare the 'Centrics Copernicus model
naturally explained retrograde motion and, to
some degree, the varying speeds of
planets. Copernicus had to keep the
epicyclesthough, there werent nearly as many!

• But, WAIT!
• A new problem emerges in this model!!!!
• While Copernicus solves the first two
  conundrums, he creates a new one
• PARALLAX!!!!

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ParallaxConundrum 3

• If the Earth were actually on an orbit around the
  sun, why wasnt a parallax effect observed????
• What other issues may have posed problems for the
  sun-centered model?

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WHO WON????

• The story continues.