Reaction Rates

• cross section
• mean free path and time
• energy production rate
• hydrogen burning rates

Stellar Evolution on the Main Sequence

• hydrogen burning and mean particle mass
• stellar response: main sequence brightening
  • early work: Schwarzschild, Howard, and Harm (1957)
  • modern solar model predictions for luminosity and radius evoution (Bahcall+ 2001)
• test: young solar twins
• consequence: faint young sun
  • paradox
  • possible solutions, e.g., Sagan and Mullen (1972)