Plan for today
  • Motivation
   –Why is astronomy interesting?
   –A brief history of the Universe
   –Is astronomy relevant?
  • Goals for the class
  • Class logistics
     Why is astronomy interesting?
   • A question to think about
     What substance (molecule) are people mostly made 
      of?
       A. Fat
       B. Water
       C. DNA
       D. Protein
     Answer: here
  People are mostly water!
  (98% of molecules)
                            People as atoms
     What element are people mostly made of (If you could 
        count the number of each type of atom in your body, 
        which one would get the most of)?
         A. Hydrogen
         B. Carbon
         C. Nitrogen
         D. Oxygen
         E. Iron
     Answer: here
    Water is H O, so people are mostly 
              2
    Hydrogen (63%), then Oxygen (24%)
                             People by weight 
        •  Different atoms are made up of different numbers of protons and 
           neutrons, and thus have different masses (protons and neutrons have 
           about the same mass and electrons hardly count for any mass).
             – Hydrogen:  1 proton
             – Carbon: 6 protons + 6 neutrons
             – Nitrogen: 7 protons + 7 neutrons
             – Oxygen: 8 protons + 8 neutrons
        What element makes up most of the
             mass of people?
             A. Hydrogen
             B. Carbon
             C. Nitrogen
             D. Oxygen
             E. Iron
    Oxygen (>50% of mass!)
             Where do we come from?
       When were the oxygen atoms in our bodies 
           assembled (when were the protons, neutrons, 
           and electrons put together?
          A.  Within the past day, e.g. from food you ate
          B.  Within the past century, e.g. when you were born
          C.  When the Sun and Earth were formed, about 4.5 
              billion years ago
          D.  Before the Sun was formed but after the beginning of 
              the Universe
          E.  They have existed since the beginning of the 
              Universe