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Chapter 10 Our Star.doc

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Natural Science
NATS 1740
Randy Hoffman

Chapter 10 Our Star 10.1 A closer look at the sun • Why does the Sun shine? • What is the suns structure? - 19 century suggested sun generates energy by slowly contracting in size (gravitational contraction) or (Kelvin-Hemholtz contraction) - Flaw because this determined sun shines for 25 million years but fossils on earth older than that Why does the sun shine? 2 - Einstein’s theory of relativity E=mc How Fusion started - We learned that sun converts mass into energy via nuclear fusion  Requires extremely high temperatures and density - Gravitational contraction released the energy that made the Suns core hot enough for fusion The stable sun - Sun shines today because it has achieved 2 kinds of balances that keeps its size and energy output stable - Gravitational equilibrium (hydrostatic): is between the outward push or internal gas pressure and the inward pull of gravity - Everywhere inside the sun, the outward push of pressure balances the inward pull of gravity - Energy balance: between rate at which fusion releases energy in t he suns core and rate at which the suns surface radiates this energy into space What is the suns structure? Basic properties of the sun - Sunspots: dark spots on suns surface - 300,000 times mass of the earth - Does not rotate at the same rate as a spinning ball - Power: rate at which energy is used or released - Luminosity: total power output The Suns atmosphere - Solar wind: the stream of charged particles continually blown outward in all directions - Corona: outermost layer of the sun, several million km from visible surface - Chromospheres: 10,000K middle layer of the sun radiates most of UV rays - Photosphere: lowest layer, visible surface of sun, temperature under 6000K - Find sunspots in the photosphere - The suns upper atmosphere is much hotter than the visible surface or photosphere but density is much lower The Suns interior - Convection zone: where energy generate in the solar core travels upward, transported by the rising of hot gas and falling of cool gas - Radiation zone; where energy moves outward primarily in the form of photons of light - Inside the sun, temperature rises with depth reaching 15 million K in the core 10.2 Nuclear Fusion in the Sun − Nuclear fission: splitting an atom − Nuclear fusion: fusing 2 or more nuclei into 1 How does nuclear fusion occur in the sun? - Strong force: force that binds protons and neutrons together in atomic nuclei is the only force in nature that can overcome the electromagnetic repulsion between 2 positively charged nuclei - Positively charged nuclei fuse together if they pass close enough for the strong force to overpower electromagnetic repulsion - The high temperatures and pressures in solar core enough to fuse hydrogen nuclei into helium nuclei  High temperature for nuclei to collide at high speeds  High pressure necessary, without it hot plasma of solar core would simply explode The proton-proton chain - Step 1: 2 protons fuse to make a deuterium nucleus (1 proton and 1 neutron) occurs twice in reaction - Step 2: the deuterium nucleus and a proton fuse to make a nucleus of helium-3 (2 protons
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