10.2 Nuclear Fusion in the Sun
Nuclear fusion High temperature enables nuclear fusion to happen in the core of
the Sun; high density ensures it happens often enough to power the
• Sun releases energy by fusing four hydrogen nuclei into one helium nucleus, which
has less mass than four hydrogen nuclei do.
• The difference in mass is released as energy (E=mc2), in the form of gamma-ray
• Energy starts out in the core of the Sun as gamma ray photons.
Proton-proton chain the proton-proton chain is how hydrogen fuses into helium
• IN: 4 protons
• OUT: 1 H4 nucleus, 2 neutrinos, 2 gamma rays, 2 positrons (which collide with 2
electrons, making more gamma rays)
• Total mass is 0.7% lower (4 million tons of matter converted to energy every second
inside the Sun!)
Solar Thermostat Decline (rise) in core temperat