Slide Number 1Slide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16 Hinode Observations of Granules (Courtesy A. Title)Slide Number 18 SunspotsSlide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37 The Solar CycleSlide Number 39Slide Number 40 The Solar Cycle The Solar Cycle The Solar CycleSlide Number 44Slide Number 45Slide Number 46Slide Number 47Slide Number 48Slide Number 49Slide Number 50Slide Number 51Slide Number 52Slide Number 53Slide Number 54Slide Number 55 Coronal Mass EjectionsSlide Number 57Slide Number 58Slide Number 5926 September, 1999The SunStructure of the SunPhysical processes within the SunThe Active SunESS 200CThe SunLectures 4 and 5• The north and south poles are at opposite ends of the rotation axis.• Because of the 7° tilt of the axis we are able to see the north pole for half a year and the south pole for the other half.• West and east are reversed relative to terrestrial maps. When you view the Sun from the northern hemisphere of the Earth you must look south to see the Sun and west is to your right as in this picture.• The image was taken in Hα. The bright area near central meridian is an active region. The dark line is a filamentThe Structure of the Sun31 December 2005• Age = 4.5 x 109years• Mass = 1.99 x 1030 kg.• Radius = 696,000 km ( = 696 Mm)• Mean density = 1.4 x 103kg m-3( = 1.4 g cm-3)• Mean distance from Earth (1 AU) = 150 x 106km ( = 215 solar radii)• Surface gravity = 274 m s-2• Escape velocity at surface = 618 km s-1• Radiation emitted (luminosity) = 3.86 x 1026W• Equatorial rotation period = 27 days (varies with latitude)• Mass loss rate = 109kg s-1• Effective black body temperature = 5785 K• Inclination of Sun's equator to plane of Earth's orbit = 7°• Composition: 90% H, 10% He, 0.1% other elements (C, N, 0,...)2 January 2006•The Spectral Radiance of the Surface of the Sun as a Function of Wavelength– The photosphere radiates like a black body at 6000 °K–The Stefan-Boltzman law gives where R is the integrated radiation, T is the black body temperature and4TRσ=4281067.5−−−×= Kwmσ• The Solar Structure– Core– Radiative Zone– Interface Zone– Convection Zone– Photosphere– Chromosphere– Transition Zone– Corona– Solar Wind22 December 2006•Properties of the RegionsCore - Nuclear reactionsRadiative Zone - Energy transfer by photonsInterface region - Bottom of convection zoneConvective zone - Heat transfer by fluid motionPhotosphere - Opaque to radiation from below. Emits most of the Sun’s light (1023m-3, 4200K)Chromosphere - Region of rapid rise in temperature (1017m-3, 20,000K)Transition region - Bottom of coronaCorona - Very hot outer envelope of Sun (1015m-3near the Sun to 107m-3near the Earth, 2x106K)2 January 2006•Dimensions of Interior Regions– The boundaries of the core, radiative and convective zones are roughly located at .25 and .75 solar radius– The photosphere is about 500 km thick– The chromosphere is about 2500 km thick20 January 2006• Nuclear Reactions in the Coreγ20 January 2006•Details of the Nuclear Reaction– When the temperature is above 10 million K two protons fuse to create an unstable particle that immediately decays into a deuterium nucleus, a positron, and a neutrino.– The positron is annihilated by an electron giving off two gamma rays.– A hydrogen atom immediately combines with the deuterium creating a He3nucleus and a gamma ray.–Two He3nuclei eventually combine creating a helium nucleus (alpha particle) and two protons– The average time for each step is quite different The first step takes 14 million years The second step takes about 6 seconds The third step takes 1 million years– Overall six protons interact producing one helium nucleus, two neutrinos, two positrons, five gamma rays and two protons– Altogether 0.7% of the mass of four protons appears as energy• Helioseismology– Use Doppler shift in absorption line to monitor vertical velocity of points on Sun’s surface– Fourier transform time series to get wave frequencies– Fourier transform spatial profiles to get wavelengths– Different modes penetrate to different depths depending on sound velocity (temperature)– Adjust the model to predict the observed mode structure2 January 2006• An Example of Surface Oscillations– The Sun oscillates globally.– Measure the Doppler shift in the center of an absorption line at points – Translate the frequency shift into a vertical velocity ( a few cm/s)– Plot time series of the velocity at each point.– Fourier transform along a vertical line to get wavelength– Fourier transform a given time series to get frequency spectra– Sound waves trapped between the surface and a given depth depend on the order of the spherical harmonic.2 January 2006•Helioseismology–The core rotates ridgidly but the convection zone is rotatingdifferentially (faster at the equator). This shows up at the surface(26 days at the equator and 37 days at the poles).22 December 2006•The Radiative Zone– Gamma rays emitted by the nuclear reactions travel in all directions from the core– There is a net flux of radiation towards the surface– Upward moving photons encounter atoms and ions that absorb, scatter and reradiate the energy at different wavelengths– The wavelength is changed by these interactions as energy is given to particles and then reemitted– The radius of the Sun is two light seconds, but it takes about 10 million years for a photon to reach the surface– There are four processes that are important: Bound-bound transition: Excite a bound electron to a higher state in an atom and then emit an atomic line Bound-free transitions: Strip the electron from the atom leaving both with kinetic energy. The electron eventually recombines and the atom radiates the excess energy Free-free transitions: Increase the energy of an electron by absorption some or all of the energy of a photon Scattering: Alter the direction of propagation of a photon by interaction with an ion or electron2 January 2006•The