How did astronomy start?

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Department
Astronomy & Astrophysics
Course
AST201H1
Professor
Michael Reid
Semester
Winter

Description
Lecture  2:  Kepler’s  Law  and  the  History  of  Astronomy     *Term  -­‐Star:  an  object  that  generates  energy  by  nuclear  fusion;  i.e.  the  Sun   How  did  Astronomy  start?   • The  oldest  science  for  humans;  people  wanted  to  learn  astronomy  for  more   practical  reasons  rather  than  to  know  what  is  the  universe   • Ancient  astronomy  was  geocentric  or  Earth-­‐centered   o Earth  being  the  center  of  the  universe;  there  is  only  five  planets;  Sun   is  not  considered  as  a  star   § Everything  is  revolved  around  the  Earth   o Pythagorean  ideal  of  circular  motion     § The  orbits  are  in  perfect  circle  –  Aristotle’s  idea  of  heaven     §                                                                                 • Ancient  Astronomy  based  on  the  principle  of  “Saving  the  appearance”   o It’s  about  replicate  what  is  happening  around  us,  not  what  actually   happened  around  us     o Occam’s  Razor  –  simplicity  in  answer     § We  tend  to  prefer  simpler  answer     • Nicholas  Copernicus,  1473-­‐1543   o Copernican  Revolution     § NO  epicycles  –  everything  orbits  around  the  Sun       • Galileo  Galilei,  1564-­‐  1642   o The  Modern  Scientific  Method  should  be  a  cycle                             • Kepler  and  Kepler’s  Law  –  finding  the  Copernican  Model  was  a  lot  simpler     o Kepler’s  First  Law  –  (*error  in  the  law  –  it  is  not  the  Sun  who  is  at   the  focus  of  the  ellipse)   § The  orbit  of  each  planet  around  the  Sun  is  an  ellipse  with  the  Sun   at  one  focus,  nothing
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