AST- 105 1st EditionLecture 8Outline of Last LectureI. The SunII. The Structure of the SunOutline of Current LectureI. Hydrostatic EquilibriumII. Nuclear FusionIII. Nuclear Energy SourceIV. Hydrogen FusionCurrent Lecture I. Hydrostatic Equilibriuma. Standard Solar Model- computer model for the interior structure of the Suni. Based on the laws of gravity, gas dynamics, and energy transport.ii. The Sun is in equilibrium; therefore, it only changes slowlyb. Hydrostatic Equilibrium- outward gas pressure force balances inward force of gravityi. The pressure below each layer of the Sun must support the weight of that layer plus the weight of the gas above it. 1. Therefore, pressure decreases outward. II. Nuclear Fusion- the energy generation mechanism that can power the Sun for billions of years.a. Thermal Equilibrium- energy radiated from the photosphere of the Sun is replaced by an internal energy releasei. Ordinary burning (oxidation) can only power the Sun for a few thousand years. 1. The Sun needs an energy source that lasts billions of years. a. Therefore, nuclear fusion is necessary. III. Nuclear Energy Sourcea. The gas inside the Sun is in an ionized state- where electrons are stripped from the nuclei.b. Nuclear Fusion uses a combination of nuclei to produce heavier nuclei with the release of energy.i. Fusion occurs only when the nuclei move fast enough to overcome electrical repulsive force.1. This requires temperatures of > 10^7 K.IV. Hydrogen Fusion- 4 Hydrogen nuclei (protons) fuse to form 1 helium nucleusa. 4 H 1 He + energyb. Part of the mass of H is converted to energy according to Einstein’s formulai. E = mc^2E= energym=mass converted to Ec= speed of lightii. Energy is in the form of high speed particles and gamma rays.c. Hydrogen fusion can power the Sun for another 5 billion
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