AST201H1 Lecture Notes - Lecture 2: Thermostat, Solar Core, Radiation

• School: UTSG
• Department: Astronomy & Astrophysics
• Course: AST201H1
• Professor: Michael Reid

Document Summary

Photons are green when they leave sun"s surface. Fundamental forces of nature : strong force, electromagnetic, weak force, gravity. The sun was made mostly of hydrogen, a little helium, and tiny amounts of other elements. Sun began to shine about 4. 5 billion yrs ago when gravitational contraction made its core hot enough to sustain nuclear fusion. It has shined steadily ever since bc of 2 types of balance: 1. Gravitational equilibrium: a balance btw the outward push of pressure and inward pull of gravity: 2. Energy balance: btw the energy released by fusion in the core & the energy radiated into space from the sun"s surface. The hydrogen fusion reaction transforms 4 hydrogen nuclei (protons) into one helium nucleus (containing. Gamma rays and subatomic particles known as neutrinos and positrons carry off the energy released in the reaction. Fusion of hydrogen into helium generates energy bc a helium nucleus has less mass.