NATS 1740 Study Guide - Radiation Zone, Photosphere, Thermostat

• School: York University
• Department: Natural Science
• Course: NATS 1740
• Professor: Patrick Hall

Document Summary

Why does the sun shine: the sun shines because gravitational equilibrium (pressure balancing gravity) keeps its core hot and dense enough to release energy through nuclear fusion. How does nuclear fusion occur in the sun: fusion of hydrogen into helium, which occurs via the proton proton chain, gravitational equilibrium acts as a thermostat that keeps the fusion rate steady. How do we know what is happening inside the sun: theoretical models, use known laws of physics and then check the models against observations and studies. How does the energy from fusion get out of the sun: energy moves through the deepest layers of the sun the core and the radiation zone in the form of randomly bouncing photons. After energy emerges from the radiation zone, convection carries it the rest of the way to the photosphere, where it is radiated into space as sunlight. If a star cools, it shrinks because lower temperature means less pressure to resist gravity.