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Our Sun – Our Star

Our Sun – Our Star. Image credit: JAXA. OU-L P SC 100 Spring, 2009 1/81. Diameter: 1,400,000 km = 864,000 miles = 4.5 light-seconds. 1,300,000 Earths could fit inside!. 109 Earths would fit across the diameter of the sun. OU-L P SC 100 Spring, 2009 2/81.

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Our Sun – Our Star

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  1. Our Sun – Our Star Image credit: JAXA OU-L P SC 100 Spring, 2009 1/81

  2. Diameter: 1,400,000 km = 864,000 miles = 4.5 light-seconds 1,300,000Earths couldfit inside! 109 Earths would fit across the diameter of the sun OU-L P SC 100 Spring, 2009 2/81

  3. Mass: 2 x 1030 kg or 330,000 timesEarth’s mass Density: 1.41g/cm3 OU-L P SC 100 Spring, 2009 3/81

  4. What planethas this samecomposition? OU-L P SC 100 Spring, 2009 4/81

  5. Surface temp: 5800 K, 5500oC,11,000oF Luminosity – totalenergy output at allwavelengths= 4 x 1026 watts/second (more than 6 molesof 100 watt light bulbs) OU-L P SC 100 Spring, 2009 5/81

  6. 4.5 million metric tons of H are converted to He every second • Expected lifetime: 10 billion years • Distance from earth: 1 A.U. = 93,000,000 miles = 150,000,000 km = 8.33 light minutes OU-L P SC 100 Spring, 2009 6/81

  7. 1 rotation takes 27.5 days at the equator, but 31 days at the poles! (Differential rotation) • How was this determined? OU-L P SC 100 Spring, 2009 7/81

  8. Image Credit: SOHO OU-L P SC 100 Spring, 2009 8/81

  9. OU-L P SC 100 Spring, 2009 9/81

  10. The Sun’s Structure • 3InteriorLayers • The core produces the energy • The radiative zone • The convective zone • 3AtmosphereLayers • Photosphere • Chromosphere • Corona OU-L P SC 100 Spring, 2009 10/81

  11. OU-L P SC 100 Spring, 2009 11/81

  12. OU-L P SC 100 Spring, 2009 12/81

  13. The Core • 16,000,000 K(a star’s core must be at least 8,000,000 K to start fusing H to He. • no real atoms,only a soup of protons, electrons, and some larger atomic nuclei (He and C). • all radiation produced isgamma() OU-L P SC 100 Spring, 2009 13/81

  14. Radiative Layer • not hot enough for fusion • normally transparent gases have become opaque to light. • Photons of light bounce from one atom to another in a “random walk”, like a gigantic pinball game. OU-L P SC 100 Spring, 2009 14/81

  15. Radiative Layer • A given photon may take 100,000 years to reach the next layer. • As photons travel, they slowly lose energy, shifting down towards the X-ray region of the spectrum. • Temperature of this layer falls with increasing distance from core. OU-L P SC 100 Spring, 2009 15/81

  16. Convective Zone • Still hot enough to be opaque to light. • Currents of gas move vertically, like water boiling in a pan. • Energy is transported by convection, not by radiation. • This layer is like earth’s mantle. OU-L P SC 100 Spring, 2009 16/81

  17. OU-L P SC 100 Spring, 2009 17/81

  18. The tops ofconvection cellscan be seennear the sunspots.They are calledgranules, orgranularity. Image Credits: SOHO/NASA/ESA and JAXA OU-L P SC 100 Spring, 2009 18/81

  19. Granularity movie http://apod.nasa.gov/apod/ap090405.html OU-L P SC 100 Spring, 2009 19/81

  20. The Photosphere • Innermost of the sun’s atmosphere layers. • Gas cools enough that it becomes transparent to light. • Sunlight originates from this layer. This is the surface that we see. • Only 300 km thick. OU-L P SC 100 Spring, 2009 20/81

  21. Actualcolor of photo- sphere … is slightly greenish. OU-L P SC 100 Spring, 2009 21/81

  22. The Chromosphere • 2nd atmosphere layer. • Glows in red H- light (the red line from the level 3 level 2 electron transition in H atoms). • Filters out the greenish color of the photosphere, so we see yellow light. • Several thousand kilometers thick. OU-L P SC 100 Spring, 2009 22/81

  23. Image Credit: SOHO/NASA/ESA OU-L P SC 100 Spring, 2009 23/81

  24. The Corona • Millions of kilometers thick, but extremely low density. • Sun’s magnetic field agitates corona, raises temperature back up to about 2,000,000 K. • Only visible during a total solar eclipse, or from space with specially designed telescopes. OU-L P SC 100 Spring, 2009 24/81

  25. OU-L P SC 100 Spring, 2009 25/81

  26. Features on the Sun’s Surface • Produced by sun’s magnetic field. • Prominences & flares. • Sunspots • Coronal Holes • Coronal Mass Ejections OU-L P SC 100 Spring, 2009 26/81

  27. Differential Rotation • Differential rotation winds up and tangles the magnetic field, resulting in surface storms. • Process is not very well understood. OU-L P SC 100 Spring, 2009 27/81

  28. OU-L P SC 100 Spring, 2009 28/81

  29. OU-L P SC 100 Spring, 2009 29/81

  30. There’s still a lot we don’t know • Why doesn’t the sun have activity all the time? The magnetic field should be winding up and tangling constantly. • Does the sun produce the same strength of magnetic field all the time? • Is it structured differently at some times than at others? OU-L P SC 100 Spring, 2009 30/81

  31. Prominences & Flares • When a loop of the sun’s magnetic field projects out from the surface, some of the hot gas from the photosphere may flow along the field lines in arcs or loops, called prominences. OU-L P SC 100 Spring, 2009 32/81

  32. A loop prominence – lets usvisualize the magnetic field. Image Credit: TRACE/NASA OU-L P SC 100 Spring, 2009 33/81

  33. Image Credit: SOHO/NASA/ESA OU-L P SC 100 Spring, 2009 35/81

  34. Flares • Sometimes, the magnetic field lines disconnect from the sun. Hot gas trapped inside the new loop of magnetic field travels outward from the sun as a solar flare. OU-L P SC 100 Spring, 2009 36/81

  35. Image Credit: SOHO/NASA/ESA OU-L P SC 100 Spring, 2009 37/81

  36. Sun spots • Where the loops of magnetic field penetrate the sun’s surface, they cool it. • Sunspots occur in pairs of (+) and (-) polarity. • Sunspots are still about 3500 K – hot enough to melt anything on the earth, but 2000 K cooler than the surrounding surface. OU-L P SC 100 Spring, 2009 38/81

  37. OU-L P SC 100 Spring, 2009 39/81

  38. OU-L P SC 100 Spring, 2009 40/81

  39. Umbra Penumbra OU-L P SC 100 Spring, 2009 41/81

  40. Sunspot Cycle • The number of sunspots varies from year to year, along with the overall magnetic activity of the sun. • We’re used to hearing of an 11 year cycle. That’s only for the overall number of sunspots. OU-L P SC 100 Spring, 2009 42/81

  41. Sunspot Cycle • The real cycle is 22.2 – 22.4 years long, and includes 11 years of the magnetic field with (+) polarity, then another 11 years with (-) polarity. • We also see sunspots migrate from high latitudes to nearer the equator as the cycle progresses. OU-L P SC 100 Spring, 2009 43/81

  42. OU-L P SC 100 Spring, 2009 44/81

  43. You are here OU-L P SC 100 Spring, 2009 45/81

  44. Sometimes, the cycle quits! • 1645 to 1715, few sunspots observed. • Maunder Minimum. • Mini ice age across Europe. OU-L P SC 100 Spring, 2009 46/81

  45. OU-L P SC 100 Spring, 2009 47/81

  46. Coronal Holes • Actual holes or windows in the sun’s corona • Solar wind can easily blow through. • When one of these points towards the earth, the velocity and density of the solar wind increases. OU-L P SC 100 Spring, 2009 48/81

  47. A coronal hole – a window to the interior. Image Credit: SOHO/NASA/ESA OU-L P SC 100 Spring, 2009 49/81

  48. You can seethe solar windblowing thruseveralcoronal holes. Image Credit: SOHO/NASA/ESA OU-L P SC 100 Spring, 2009 50/81

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