The Sun and its Composition

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Department
Astronomy & Astrophysics
Course
AST201H1
Professor
Michael Reid
Semester
Winter

Description
AST201H-­‐  Stars  and  Galaxies         Professor  Michael  Reid                                                                                                                            Lecture  Notes     January  31,  2013   Lecture  8:  The  Sun   The  Sun  and  its  Composition   • To  understand  other  stars  in  the  space,  astronomers  compare  the  stars  to  the   Sun.  –  The  differences  and  similarities   • Compare  to  the  Earth,  Sun  is  relatively  large,  but  compare  to  the  other  stars   in  the  universe,  the  Sun  is  relatively  small.   • In  astronomy,  heavy  elements  and  light  elements  are  different  from  what  the   chemists  think  about  the  periodic  table   o Helium  is  considered  as  a  metal  in  astronomy     • Inside  of  the  Sun,  most  of  the  components  are  still  hydrogen     o Therefore,  the  Sun  is  mainly  made  of  light  elements     • To  know  where  some  elements  are  present  in  spectrum,  the  spectral  lines   have  to  match  up  to  the  spectrum  that  is  being  compared  to.  And  the  amount   of  black  (the  absorbed  light)  indicates  the  quantity  of  that  element   • The  sun  shines  because  it  is  converting  its  own  energy   Energy  and  Mass   • 𝐸 = 𝑚𝑐  -­‐  relationship  between  energy  and  mass   •  To  get  particles  to  overcome  their  mutual  repulsion,  they  have  to  have  A  LOT   OF  ENERGY   o Mutual   charges   –   natural   repulsion,   but   still   attract   to   each   other   gravitationally     • To   get   particles   to   overcome   natural   repulsion,   they   need   to   move   very   quickly  and  have  to  be  very  hot   o Atomic  motion  in  the  Sun  is  very  fast  –  which  means  high  temperature     o Hot  =  energetic  =  rapid  atomic  motion     § Sun’s  core  =  15  million  K                                         AST201H-­‐  Stars  and  Galaxies         Professor  Michael  Reid                                                                                                                            Lecture  Notes     • This  fusion  reaction  is  called  proton-­‐proton  or  p-­‐p  chain   o Main  source  of  energy  for  the  sun   o Nuclear  fusion  is  smashing  nuclei  together  to  form  lar
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