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An Introduction to the Physics of Our Star: The Sun

An Introduction to the Physics of Our Star: The Sun. Distance from Earth 1 AU Travel time for Light to Earth About 8 minutes Travel time for solar wind to 1 AU A few days Mean surface temperature 5800K Temperature in the Center 1.55x10 7 K. The Sun. Mass 333,000 Earth Masses

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An Introduction to the Physics of Our Star: The Sun

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  1. An Introduction to the Physics of Our Star: The Sun • Distance from Earth • 1 AU • Travel time for Light to Earth • About 8 minutes • Travel time for solar wind to 1 AU • A few days • Mean surface temperature • 5800K • Temperature in the Center • 1.55x107 K Solar Science Workshop 6/8/05

  2. The Sun • Mass • 333,000 Earth Masses • More mass than all of the other objects in the solar system combined • Diameter • 218 Earth Diameters • Average Density • 1410 kg/m3 • Composition (by mass) • 74% Hydrogen, 25% Helium, 1% other elements Sun seen in Xrays Solar Science Workshop 6/8/05

  3. The Sun Seen From Earth by Amateurs • COMMON SENSE WARNING … NEVER LOOK DIRECTLY AT THE SUN WITHOUT A PROPER FILTER !! • Looking directly at the Sun without the proper filter WILL cause permanent eye damage • Safest to use the method of projection • Project the image onto a piece of paper • Can see sunspots, and even “graph” them easily Solar Science Workshop 6/8/05

  4. The Sun Seen From Earth by Amateurs • Using a Baader solar filter • Inexpensive • Many “solar observing glasses” are made out of this material • Used to see sunspots • Similar to Mylar Solar Science Workshop 6/8/05

  5. The Sun Seen From Earth by Amateurs • Hα filters • Much more pricey • 100s-1000s of dollars • Can see features in the solar chromosphere • Used to see Prominences, filaments, flares • Very impressive Sun seen with an Hα filter Solar Science Workshop 6/8/05

  6. How Old is the Sun ? • Probably about the same age as Earth • Has it been shining brightly the entire time? • The luminosity has probably increased with time, but it has always been very bright • What is the “fuel” that keeps it shining this long? Solar Science Workshop 6/8/05

  7. The Sun’s Energy Source is ThermonuclearFusion in its Core • Proton-proton chain • Four hydrogen nuclei “fuse” to form a single helium nucleus • There is a slight loss of mass in this process which is converted to energy according to Einstein’s famous equation E = mc2 • Thermonuclear fusion occurs only at the very high temperatures at the Sun’s core • Fusion should not be confused with fission ! • Will continue to heat the Sun for another 5 billion years Solar Science Workshop 6/8/05

  8. The Proton-Proton Chain Solar Science Workshop 6/8/05

  9. The Structure of the Sun • The Interior • Core • Radiative zone • Convection zone • The Surface and Atmosphere • Photosphere • Chromosphere • corona Solar Science Workshop 6/8/05

  10. The Sun’s Interior • Hydrogen fusion takes place in a core extending from the Sun’s center to about 0.25 solar radius • The radiative zone extends to about 0.71 solar radius • Here energy travels outward through radiative diffusion • The convective zone is a rather opaque gas • Here energy travels outward primarily through convection Solar Science Workshop 6/8/05

  11. Where do the Neutrino’s and γ-ray photons go ? • Neutrino’s exit the Sun, unimpeded • Can be used to probe the solar interior • Early attempts at detecting them found that their were about 3 times less seen at Earth than there should be • THE SOLAR NEUTRINO PROBLEM ! • The gamma rays collide with matter and take millions of years to exit the Sun Solar Science Workshop 6/8/05

  12. Detecting Solar Neutrinos • Underground detectors are used to avoid interference from cosmic rays Solar Science Workshop 6/8/05

  13. The Solution to the Solar Neutrino Problem • Particle Physics gave us the answer • Solar neutrinos oscillate and the original detectors could only see certain parts of the oscillations and not all of them • New detectors were built to observe all neutrinos • Two physicists won a Nobel Prize for their work • Modern detectors are placed at different depths within the Earth to observe the actual oscillations Raymond Davis Jr. Masatoshi Koshiba Solar Science Workshop 6/8/05

  14. Solar Structure • The standard solar model • Theoretical model used to determine the physical properties of the Sun’s interior • Assumes hydrostatic and thermal equilibrium Solar Science Workshop 6/8/05

  15. Solar Oscillations • Waves can propagate through the Sun causing a variety of vibrations • Like sound waves • These are used to infer pressures, densities, chemical compositions, and rotation rates within the Sun Solar Science Workshop 6/8/05

  16. Helioseismology • The branch of science that studies solar oscillations is known as Helioseismology • The movie shows evidence of seismic activity on the Sun as seen by the SOHO MDI experiment Solar Science Workshop 6/8/05

  17. The Convection Zone • The convection zone is just outside the radiative zone. • Thickness is about 200,000 km • Turbulent convective motions occur, similar to a pot of boiling water. • Overturning (bubbling) motions inside the Sun are responsible for the granulation pattern seen on the Sun’s surface. Solar Science Workshop 6/8/05

  18. Convection Cells Solar Science Workshop 6/8/05

  19. Solar Granulation • Convection cells that are about 1000 km wide • These are part of the Sun’s atmosphere known as the Photosphere Solar Science Workshop 6/8/05

  20. Recent High-resolution Images of granulation Solar Science Workshop 6/8/05

  21. “Flowers” and Ribbons • Produced by magnetic fields Solar Science Workshop 6/8/05

  22. The photosphere is the lowest of three main layersin the Sun’s atmosphere • The Sun’s atmosphere has three main layers: the photosphere, the chromosphere, and the corona • Everything below the solar atmosphere is called the solar interior • The visible surface of the Sun, the photosphere, is the lowest layer in the solar atmosphere • The photosphere undergoes “differential” rotation Solar Science Workshop 6/8/05

  23. Limb Darkening • The edges of the Sun appear darker than that seen “straight on” • This is called limb darkening • It is due to the fact that the temperature in the photosphere decreases with altitude Solar Science Workshop 6/8/05

  24. The Origin of Limb Darkening • The light we see at the limb originated higher up in the atmosphere where it is cooler • Thus it will be less bright there Solar Science Workshop 6/8/05

  25. Sunspots • Low temperature regions • How do we know this ? • Darkest part is called the “umbra” • Just outside the umbra is the penumbra • Associated with Intense magnetic fields Solar Science Workshop 6/8/05

  26. Solar Science Workshop 6/8/05

  27. Sunspots Often Come in Groups Solar Science Workshop 6/8/05

  28. The Chromosphere • Above the photosphere is a layer of less dense but higher temperature gases called the chromosphere “Color Sphere” • characterized by spikesof rising gas • Spicules extend upward from the photosphere into the chromosphere along the boundaries of supergranules Solar Science Workshop 6/8/05

  29. Chromospheric Features:Plages and Filaments • Filaments are dark, thread-like features seen in the red light of hydrogen (H-alpha). • Dense cooler material suspended at high altitudes by magnetic fields • Plage (the French word for beach) are bright patches surrounding sunspots that are best seen in H-alpha. • associated with concentrations of magnetic fields Solar Science Workshop 6/8/05

  30. Chromospheric Features: Prominences • Same as filaments, except that they are seen from the side rather than “straight on” Solar Science Workshop 6/8/05

  31. The Corona • The outermost layer of the solar atmosphere, the corona, is made of very high-temperature gases at extremely low density • The solar corona blends into the solar wind at great distances from the Sun Solar Science Workshop 6/8/05

  32. The 11-year Sunspot Cycle Number of Sunspots versus time – they come and go every 11 years Number of Sunspots versus latitude – forms a “butterfly pattern” Solar Science Workshop 6/8/05

  33. The Maunder Minimum • Complete absence of sunspots for 50 years corresponds to a mini ice age • There is a loose correlation between global man temperature and sunspots Solar Science Workshop 6/8/05

  34. These changes are caused by convection and the Sun’s differential rotation: The Solar Dynamo Solar Science Workshop 6/8/05

  35. The Buildup of magnetic field energy must be released – how? • Coronal Mass Ejections and Flares • Releases an enormous amount of energy • A solar flare is a brief eruption of hot, ionized gases from a sunspot group • A coronal mass ejection is a much larger eruption that involves immense amounts of gas from the corona • These storms can interact with the Earth and create huge geomagnetic storms • They also accelerate particles to very high energies Solar Science Workshop 6/8/05

  36. Coronal loops expand from the surface of the Sun following a solar explosion (solar flare) on April 21, 2002 TRACE movie Solar Science Workshop 6/8/05

  37. Solar Science Workshop 6/8/05

  38. The Halloween 2003 Flares were the Largest in Modern History Perhaps the most extreme flare ever seen erupted on Nov. 4 ... IMAGES: SOHO/NASA/ESA ... and then this coronal mass ejection was hurled into space. Solar Science Workshop 6/8/05

  39. Solar Science Workshop 6/8/05

  40. Aurora The pattern of auroral light around the north and south magnetic poles is called the auroral oval. It expands and contracts over a period of hours and days, depending on geomagnetic activity. Solar Science Workshop 6/8/05

  41. Aurora in Tucson Solar Science Workshop 6/8/05

  42. Shock Waves in Space • Analogy with sonic booms • Can accelerate charged particles to very high energies • Radiation Environment ! • Space Weather Solar Science Workshop 6/8/05

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