Chapter 11The SunA bit about energySlide 4Properties of the SunSlide 6Slide 7The Structure of the SunThis picture was copied from astronomynotes.com of Nick Strobel.Slide 10Slide 11The Solar InteriorSlide 13The Radiative ZoneSlide 15The Convection ZoneGranulationThe Sun’s AtmosphereSlide 19The ChromosphereThe CoronaHow the Sun WorksPressure in the SunPowering the SunSlide 25Slide 26The Proton-Proton Chain: Step 1The Proton-Proton Chain: Step 2The Proton-Proton Chain: Step 3Solar NeutrinosSlide 31Slide 32Solar SeismologySlide 34Solar Magnetic ActivitySunspotsSlide 37Origin of SunspotsSlide 39Slide 40ProminencesSlide 42Solar FlaresSlide 44Impact of Solar FlaresHeating of the Chromosphere and CoronaSlide 47Slide 48The Zeeman EffectThe Solar WindThe Solar CycleDifferential RotationCause of the Solar CycleChanges in the Solar CycleSolar Cycle and ClimateChapter 11The Sun, Our StarCopyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.The Sun•The Sun is a star, a luminous ball of gas more than 100 times bigger than the Earth•Although seemingly quiescent from a naked eye view, telescopic observations reveal a bevy of violent activity – fountains of incandescent gas and twisting magnetic fields•The Sun’s core is equally violent with a furnace of thermonuclear fire converting hydrogen into helium to the tune of an energy production equivalent to the detonation of 100 nuclear bombs•The force of gravity keeps the Sun in check – for nowA bit about energy •The M.K.S. unit of energy is the Joule (J)•If I drop a 1 kg mass from the top of the lecture table to the floor the collision with the floor gives up about 10 J•A Watt is a J/sec•The sun has a power output of 4 x 1026 Watts•The solar constant is ~ 1.4 kW/m2 and the earth receives about 70% of that or about 1 kW/m2 •Through the atmosphere and averaged over the whole day gives us around 200 W/m2 •A gallon of gasoline is equivalent to 1.3 x 108 J•A solar power plant capable of the energy of a typical electric generating station would take up land 10 miles on a sideThe Sun•With a radius 100× and a mass of 300,000× that of Earth, the Sun must expend a large amount of energy to withstand its own gravitational desire to collapse•To understand this process requires detailed observations as well as sophisticated calculations involving computer models and the laws of physicsProperties of the Sun•The Sun’s distance from Earth (about 150 million km or 1 AU) was once measured by triangulation, but is now done by radar•Once the distance is known, its diameter (about 1.4 million km) can be found from its angular size (about 1/2 degree)Properties of the Sun•From the Sun’s distance and the Earth’s orbital period, Kepler’s modified third law gives the Sun’s mass•Mass and radius, the surface gravity of the Sun is found to be 30× that of Earth•Next, the surface temperature (5780 K) is found from the Sun’s color and the use of Wien’s law for a blackbodyProperties of the Sun•Theoretical considerations then establish the Sun as gaseous throughout with a core temperature of 15 million K•From the amount of solar energy that reaches the Earth (4 × 1026 watts), this energy must be replenished by fusion processes in its core•The Sun has plenty of hydrogen for fusion: its surface spectra shows hydrogen is 71% and 27% heliumThe Structure of the SunThis picture was copied from astronomynotes.com of Nick Strobel.From The WEBSITE: http://www.kis.uni-freiburg.de/~pnb/granmovtext1.htmlGranulation in the photosphere of our SUN. A time lapse movie.A 27 x 27 Mm2 FieldCondensed into 35 minutes“The series was observed with a fast frame selection system on June 5, 1993, at the SVST (La Palma) in cooperation with G. Scharmer (Stockholm) and G. W. Simon (Sunspot); N. Hoekzema (Utrecht), W. Mühlmann (Graz), and R. Shine (Palo Alto) were involved in the data analysis. Technical data: wavelength 468 ± 5 nm; exposure time 0.014 s; rms contrast (uncorrected) between 7 and 10.6 %. The images were registered, destretched, corrected for the telescope's point spread function, and subsonically filtered after interpolation to equal time steps. “Note: Image Not in your Text!This is what the surface of the sun looks like --- oatmeal!This picture was copied from astronomynotes.com of Nick Strobel.The Solar Interior•The low density upper layers of the Sun, where any photons created there can freely escape into space is called the photosphere•The photosphere is yellow “surface” we see with our eyes•Layers below the photosphere are opaque, photons created there are readily absorbed by atoms located thereThe Solar Interior•Theoretical calculations show that the Sun’s surface temperature and density both increase as the core is approached–The density is similar to that found at sea level on Earth at the Sun’s surface and 100× that of water at the coreThe Radiative Zone•Since the core is hotter than the surface, heat will flow outward from the Sun’s center•Near the Sun’s center, energy is moved outward by photon radiation – a region surrounding the core known as the radiative zoneThe Radiative Zone•Photons created in the Sun’s interior do not travel very far before being reabsorbed – energy created in the Sun’s center will take about 16 million years to eventually diffuse to the surface!The Convection Zone•Above the radiative zone energy is more efficiently transported by the rising and sinking of gas – this is the convection zoneGranulation•Convection manifests itself in the photosphere as granulation, numerous bright regions surrounded by narrow dark zonesThe Sun’s Atmosphere•The extremely low-density gases that lie above the photosphere make up the Sun’s atmosphereThe Sun’s Atmosphere•The density of the atmosphere decreases steadily with altitude and eventually merges with the near-vacuum of space•Immediately above the photosphere, the temperature of the atmosphere decrease but at higher altitudes, the temperature grows hotter, reaching temperatures of several million Kelvin•The reason for the increase in temperature is unknown, but speculation is that Sun’s magnetic field plays an important roleThe Chromosphere•The lower part of the atmosphere is referred to as the chromosphere–The chromosphere appears as a thin red zone around the dark disk of a totally eclipsed Sun–The red is caused by the strong red emission line of