Aristarchus from Samos (250 BC) 

  Theorized the "radical" view that the Earth
  and all the Planets revolve around the Sun:
  The Heliocentric model. The model was not
   accepted because it contradicted the "Great"
  Aristotle and predicted parallax; the change
  in the position of the stars as the Earth moves.
  Note that Aristarchus also said that stellar
  parallax will not be observed because the stars
  were very far away. A man 17 centuries ahead
  of his time!

Ptolemy (140 AD) 

  Adopted Aristotle's Geocentric(or earth-centered)
  model. All heavenly bodies move in uniform circular
  motion around the Earth. However, ... planets do not
  move in simple circular orbits around the Earth; they
  show: Retrograde Motion

 
  For almost 1,500 years all of Astronomy was summarized in Ptolemy's book
  known now as Almagest (Greatest).

Modern Astronomy: Copernicus (1500)

 
  Adopted (Aristarchus) Heliocentric model: The Sun,
  not the Earth, is at the center of the Universe. The model
  gain support because it was beautiful and elegant in its
  explanation of retrograde motion. The model was not
  totally correct, as it predicted that the planets will move in
  circular orbits around the Sun. The fine-tuning of the
  model, and the birth of Modern Astronomy, came with: 

  Tycho, Kepler, Galileo, and Newton.

Galileo's observation that the apparent size of Venus changes for different

phases provided strong evidence in support of the heliocentric system. If

Venus orbited the Earth as Aristotle believed, it would always appear

of the same size, just as the Moon does.