•Aristotle had good reasons to think the Earth stood
 still:
 –Absence of any
 detectable parallax
  
  If the Earth orbits
 the sun (rather than the reverse) then we should be able to see shifts in the positions of the stars due
 to parallax. 
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 •The amount of
 parallax is proportional to 
  
 –We now know the
 distance to the nearest star is so large that even it only has a parallax of 1 second of arc = 1/3600 deg.  1 parsec = 3.26 ly.
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