1. Stellar Structure Temperature, density and pressure decreasing Energy generation via nuclear fusion Energy transport via radiation Energy transport via convection Flow of energy Basically the same structure for all stars with approx. 1 solar mass or less. Sun

2. What would happen if the sun suddenly stopped producing energy in its center? 1.It would explode. 2.It would rapidly collapse. 3.It would gradually cool off and shrink. 4.It would gradually cool off and expand. 5.It would maintain its current structure.

3. Outward pressure of hot gas in the center balances the inward force due to gravity. Hydrostatic Equilibrium

4. Outward pressure force must exactly balance the weight of all layers above any given point in the star. This condition uniquely determines the interior structure of the star. This is why we find stable stars on such a narrow strip (Main Sequence) in the Hertzsprung-Russell diagram.

6. How does the sun produce energy in its center? 1.Through chemical burning of hydrogen (2 H + O → H 2 O). 2.Through thermonuclear fusion of helium into Carbon. 3.Through thermonuclear fusion of hydrogen into helium. 4.Through thermonuclear fission of helium into hydrogen. 5.Through thermonuclear fission of Uranium into lighter nuclei.

7. The CNO Cycle In stars slightly more massive than the sun, a more powerful energy generation mechanism than the PP chain takes over: The CNO Cycle. In the sun, energy production is dominated by direct fusion of H into He (PP chain).

8. Energy Transport Structure Inner radiative, outer convective zone Inner convective, outer radiative zone CNO cycle dominantPP chain dominant

9. Mass Sun Radiative Core, convective envelope; Energy generation through PP Cycle Convective Core, radiative envelope; Energy generation through CNO Cycle Summary: Stellar Structure