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Transcript
Chapter 14 Our Star The Sun is the Largest Object in the Solar System • The Sun contains more than 99.85% of the total mass of the solar system • If you put all the planets in the solar system, they would not fill up the volume of the Sun • 110 Earths or 10 Jupiters fit across the diameter of the Sun © 2006 Pearson Education Inc, publishing as Addison-Wesley What makes the Sun shine? • Nuclear (mass) energy makes the Sun shine E = mc2 Nuclear P.E. Luminosity = ~ 10 billion yrs 4 3 Sun releases energy by fusing four hydrogen nuclei into one helium nucleus Sun releases energy by fusing four hydrogen nuclei into one helium nucleus extra mass Neutrons are less massive than protons Total mass is 0.7% lower Mass converted to energy: E = mc2 Neutrons are less massive than protons Total mass is 0.7% lower Mass converted to energy: E = mc2 © 2006 Pearson Education Inc, publishing as Addison-Wesley © 2006 Pearson Education Inc, publishing as Addison-Wesley What is the Sun’s structure? The Stable Sun Sun is in • Gravitational Equilibrium: ✴ Pressure Out = Gravity In • Thermal Equilibrium: ✴ Energy Out (radiated) = Energy Produced (fusion) 6 © 2006 Pearson Education Inc, publishing as Addison-Wesley Radiative Zone INTERIOR: Radiative Diffusion: Energy gradually leaks out of radiation zone in form of randomly absorbed/reemitted photons The Sun’s interior has three layers: (1) core (2) radiative zone (3) convective zone Energy generated in the core of the Sun propagates outward through these different layers, and finally, through the atmosphere of the Sun. This process takes tens of thousands of years or more. © 2006 Pearson Education Inc, publishing as Addison-Wesley Solar Vibrations Convective Zone • Hot gas becomes less dense; rises • Releases heat at surface; cools; becomes less dense; sinks • “Helioseismology” • Pressure waves (sound waves) from moving gas • Cause “vibrations” of surface: detected from doppler shift • Waves change due to changing T, density with radius in Sun 10 11 Patterns of vibration on surface tell us about what Sun is like inside Solar Neutrinos • Neutrinos created during fusion fly directly through the Sun • Observations of these solar neutrinos can tell us what’s happening in core 13 © 2006 Pearson Education Inc, publishing as Addison-Wesley © 2006 Pearson Education Inc, publishing as Addison-Wesley 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 15 © 2006 Pearson Education Inc, publishing as Addison-Wesley The Sun’s atmosphere also has three layers… • • • Photosphere the layer we see, 5800 K Chromosphere the red layer observed using a hydrogen filter, 10,000 K Corona - the incredibly thin outer atmosphere, 1,000,000 K Photosphere Visible layer of the Sun Granulation caused by convection 17 Convective Cells in the Sun Chromosphere: Middle layer of solar atmosphere ~ 104 - 105 K Hot, thin gas: emission line spectrum (mostly Hα 18 © 2006 Pearson Education Inc, publishing as Addison-Wesley Spicules • Jets of hot gas extending a few 1000 km up; fall back Corona: Outermost layer of solar atmosphere ~1 million K 20 © 2006 Pearson Education Inc, publishing as Addison-Wesley The corona, the outermost part of the Sun’s atmosphere, is characterized by its high temperature and low density Solar wind: A flow of charged particles from the surface of the Sun The Sun also ejects a stream of charged particles into space known as the solar wind © 2006 Pearson Education Inc, publishing as Addison-Wesley Sunspots The annual change in numbers of sunspots reveals that the Sun experiences an 11-year Sun Spot cycle Are cooler (4000 K) than other parts of the Sun’s surface (6000 K) Maximum number Minimum number Are regions with strong magnetic fields Stars and their Properties Measuring Distances • Use parallax to measure distances to (nearby) stars 26 27 The Magnitude Scale Apparent Magnitude is a number that represents the apparent brightness of stars as seen on Earth How bright a star appears depends on both how much light it releases (its actual brightness or luminosity) and how far away it is (distance) according to the inverse square law Apparent Brightness = Luminosity: L The LARGER the number the dimmer the object will appear from Earth L Surface Area = L 4πd2 Surface Area: 4πd2 Note we use the letter “m” for apparent magnitude 28 True Brightness (Luminosity) If you pass white light through a prism, it separates into its component colors. long wavelengths • Dim stars are common • Luminous stars are rare R O Y G B I V short wavelengths 30 spectrum Spectra Three Stars: Different Temperatures A B C 32 Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types O B A F G K M Hot (25,000 K) Cool (3500K) This is a TEMPERATURE sequence © 2006 Pearson Education Inc, publishing as Addison-Wesley Stars are classified by their spectra as O, B, A, F, G, K, and M spectral types • • • • OBAFGKM hottest (>25,000 K) to coolest (3500 K) bluish to reddish An important sequence to remember: – Oh Be a Fine Guy (or Girl), Kiss Me – Oh Boy, An F Grade Kills Me The Hertzsprung-Russell (H-R) diagram identifies a definite relationship between temperature and absolute magnitude • Main Sequence stars are found in a band from the upper left (hot, bright) to the lower right (cool, dim) • 90% of stars are in this stage of their lives • Includes our sun HR DIAGRAM Large radius • Stars fall into one of 4 groups (based on L, T relation) –Main Sequence –Supergiants –Giants –White Dwarfs Small radius © 2006 Pearson Education Inc, publishing as Addison-Wesley