Chapter 10 Our Star Copyright 2009 Pearson Education Inc Fission Fusion Big nucleus splits into smaller pieces Small nuclei stick together to make a bigger one Nuclear power plants Sun stars Copyright 2009 Pearson Education Inc High temperatures enable nuclear fusion to happen in the core Copyright 2009 Pearson Education Inc The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus Copyright 2009 Pearson Education Inc IN 4 protons OUT 4He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0 7 lower Copyright 2009 Pearson Education Inc Thought Question What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy A The core would expand and heat up slightly B The core would expand and cool C The Sun would blow up like a hydrogen bomb Copyright 2009 Pearson Education Inc Thought Question What would happen inside the Sun if a slight rise in core temperature led to a rapid rise in fusion energy A The core would expand and heat up slightly B The core would expand and cool C The Sun would blow up like a hydrogen bomb Solar thermostat keeps the rate of fusion steady Copyright 2009 Pearson Education Inc Solar Thermostat Decline in core temperature causes fusion rate to drop so core contracts and heats up Copyright 2009 Pearson Education Inc Rise in core temperature causes fusion rate to rise so core expands and cools down How does the energy from fusion get out of the Sun Copyright 2009 Pearson Education Inc Energy gradually leaks out of the radiation zone in the form of randomly bouncing photons Copyright 2009 Pearson Education Inc Convection rising hot gas takes energy to the surface Copyright 2009 Pearson Education Inc Bright blobs on photosphere where hot gas reaches the surface Copyright 2009 Pearson Education Inc How do we know what is happening inside the Sun Copyright 2009 Pearson Education Inc We learn about the inside of the Sun by making mathematical models observing solar vibrations observing solar neutrinos Copyright 2009 Pearson Education Inc Patterns of vibration on the surface tell us about what the Sun is like inside Copyright 2009 Pearson Education Inc Data on solar vibrations agree with mathematical models of solar interior Copyright 2009 Pearson Education Inc Neutrinos created during fusion fly directly through the Sun Observations of these solar neutrinos can tell us what s happening in the core Copyright 2009 Pearson Education Inc Solar neutrino problem Early searches for solar neutrinos failed to find the predicted number Copyright 2009 Pearson Education Inc Solar neutrino problem Early searches for solar neutrinos failed to find the predicted number More recent observations find the right number of neutrinos but some have changed form Copyright 2009 Pearson Education Inc What have we learned How does nuclear fusion occur in the Sun The core s extreme temperature and density are just right for the nuclear fusion of hydrogen to helium through the proton proton chain Gravitational equilibrium acts as a thermostat to regulate the core temperature because the fusion rate is very sensitive to temperature Copyright 2009 Pearson Education Inc What have we learned How does the energy from fusion get out of the Sun Randomly bouncing photons carry it through the radiation zone The rising of hot plasma carries energy through the convection zone to the photosphere How do we know what is happening inside the Sun Mathematical models agree with observations of solar vibrations and solar neutrinos Copyright 2009 Pearson Education Inc 10 3 The Sun Earth Connection Our goals for learning What causes solar activity How does solar activity affect humans How does solar activity vary with time Copyright 2009 Pearson Education Inc What causes solar activity Copyright 2009 Pearson Education Inc Solar activity is like weather on Earth Sunspots Solar flares Solar prominences All these phenomena are related to magnetic fields Copyright 2009 Pearson Education Inc Sunspots Are cooler than other parts of the Sun s surface 4000 K Are regions with strong magnetic fields Copyright 2009 Pearson Education Inc Zeeman Effect We can measure magnetic fields in sunspots by observing the splitting of spectral lines Copyright 2009 Pearson Education Inc Charged particles spiral along magnetic field lines Copyright 2009 Pearson Education Inc Loops of bright gas often connect sunspot pairs Copyright 2009 Pearson Education Inc Magnetic activity causes solar flares that send bursts of X rays and charged particles into space Copyright 2009 Pearson Education Inc Magnetic activity also causes solar prominences that erupt high above the Sun s surface Copyright 2009 Pearson Education Inc The corona appears bright in X ray photos in places where magnetic fields trap hot gas Copyright 2009 Pearson Education Inc How does solar activity affect humans Copyright 2009 Pearson Education Inc Coronal mass ejections send bursts of energetic charged particles out through the solar system Copyright 2009 Pearson Education Inc Charged particles streaming from the Sun can disrupt electrical power grids and disable communications satellites Copyright 2009 Pearson Education Inc How does solar activity vary with time Copyright 2009 Pearson Education Inc The number of sunspots rises and falls in 11 year cycles Copyright 2009 Pearson Education Inc The sunspot cycle has something to do with the winding and twisting of the Sun s magnetic field Copyright 2009 Pearson Education Inc What have we learned What causes solar activity The stretching and twisting of magnetic field lines near the Sun s surface causes solar activity How does solar activity affect humans Bursts of charged particles from the Sun can disrupt communications satellites and electrical power generation How does solar activity vary with time Activity rises and falls in 11 year cycles Copyright 2009 Pearson Education Inc 11 1 Properties of Stars Our goals for learning How do we measure stellar luminosities How do we measure stellar temperatures How do we measure stellar masses Copyright 2009 Pearson Education Inc How do we measure stellar luminosities Copyright 2009 Pearson Education Inc Brightness of a star depends on both distance and luminosity Copyright 2009 Pearson Education Inc Luminosity Amount of power a star radiates energy per second watts Apparent brightness Amount of starlight that reaches Earth energy per second per square meter Copyright 2009 Pearson Education Inc Thought Question These
View Full Document
Unlocking...