Overview
This lecture covers the structure of the Sun, focusing on how the Sun generates its energy and light through nuclear fusion, specifically the proton-proton chain.
How the Sun Produces Light
- The Sun generates light by nuclear fusion, not by burning or fire.
- Fusion combines small atoms (hydrogen) into larger atoms, releasing energy.
- This differs from fission, which splits large atoms (used in nuclear power plants).
Location and Conditions for Fusion
- Fusion requires extremely high temperature and density, only found in the Sun’s core.
- The Sun’s core is where hydrogen fusion happens, acting as its power plant.
Hydrogen Fusion and the Proton-Proton Chain
- The Sun mainly fuses hydrogen atoms (protons) through the proton-proton chain.
- At high temperatures, hydrogen atoms lose their electrons and become ions, creating a plasma.
- Four protons (hydrogen nuclei) fuse in the core to eventually form a new atom.
Products of the Fusion Process
- During fusion, some protons turn into neutrons, creating new particles.
- The process produces two gamma-ray photons (high-energy light), two neutrinos (nearly non-interactive particles), and two positrons (antielectrons).
- Positrons (antimatter electrons) quickly encounter electrons and annihilate, releasing more gamma-ray photons.
- In total, four gamma-ray photons are produced per cycle of the proton-proton chain.
Key Terms & Definitions
- Fusion — Combining small atomic nuclei to form a larger nucleus, releasing energy.
- Fission — Splitting a large atomic nucleus into smaller parts, releasing energy.
- Core (of the Sun) — The central region where temperatures and densities are high enough for fusion.
- Ion — An atom missing one or more electrons, resulting in a charged particle.
- Plasma — A state of matter made of ions and free electrons.
- Proton-Proton Chain — The main fusion process in the Sun where hydrogen nuclei fuse to form helium.
- Gamma Ray — The highest energy form of light produced during nuclear reactions.
- Neutrino — A nearly massless, weakly interacting particle produced in fusion.
- Positron — The antimatter counterpart to the electron, with a positive charge.
- Annihilation — Destruction of a particle and its antiparticle, converting their mass to energy.
Action Items / Next Steps
- Read the posted "History of the Solar System" file on Canvas.