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  • 1. Our Sun – Our Star
  • 2.  
  • 3. 109 Earths would fit across the diameter of the sun!! Diameter: 1,400,000 km, 864,000 miles 4.5 light-seconds 1,300,000 Earths could fit inside!
  • 4. Mass: 2 x 10 30 kg or 330,000 times Earth’s mass!! Density: 1.41 g/cm 3
  • 5. What planet has this same composition?
  • 6. Surface temp: 5800 K, 5500 o C, 11,000 o F
  • 7. Trivia…
    • 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 !
  • 8. Trivia
    • 1 rotation takes 27.5 days at the equator, but 31 days at the poles! Now that’s differential rotation. How was this determined?
  • 9. That’s right – sunspots!
  • 10. The Sun’s Structure
    • 3 Interior Layers
            • The core produces the energy
            • The radiative zone
            • The convective zone
    • 3 Atmosphere Layers
            • Photosphere
            • Chromosphere
            • Corona
  • 11.  
  • 12. A. The Core
    • 16,000,000 K (a star’s core must be at least 8,000,000 K to start fusing H to He.
    • so hot that there are no real atoms , only a soup of protons, electrons, and some larger atomic nuclei (He and C).
  • 13.  
  • 14. B. Radiative Layer
    • Made of H, He gases.
    • A given photon may take 100,000 years to reach the next layer.
    • Temperature of this layer falls with increasing distance from core, it is not hot enouh for fusion to take place.
  • 15.  
  • 16. C. Convective Zone
    • Made of H, He gases.
    • Currents of gas move vertically, like water boiling in a pan.
    • Energy is transported by moving hot mass (convection), not by radiation.
    • This layer is like earth’s mantle.
  • 17.  
  • 18. The tops of convection cells can be seen near the sunspots. They are called granules , or granularity.
  • 19.  
  • 20. 3 Atmosphere Layers
    • A. The Photosphere
    • The innermost of the sun’s atmosphere layers.
    • H, He gas finally cools and is the origin of most of the visual light .
    • Only 300 km thick.
  • 21. Actual color of photo- sphere … is slightly greenish.
  • 22. B. The Chromosphere
    • 2 nd atmosphere layer.
    • Glows in red light
    • Tends to filter out the slightly greenish color of the photosphere , so we see yellow light from sun.
    • Several thousand kilometers thick.
  • 23.  
  • 24. C. 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 .
    • We can only study corona during a total solar eclipse, or from space with specially designed telescopes.
  • 25.  
  • 26. Features on the Sun’s Surface
    • All features are produced by sun’s wacky magnetic field .
    • Prominences & flares.
    • Sunspots
    • Coronal Holes
    • Coronal Mass Ejections
  • 27. Differential Rotation
    • If the sun were solid and magnetic field rotated in an orderly way, there would be no storms or surface features on the sun, but…
    • … differential rotation winds up and tangles the sun’s magnetic field, resulting in surface storms.
    • Process is not very well understood.
  • 28.  
  • 29.  
  • 30. There’s still a lot we don’t know
    • For example, why doesn’t the sun have activity all the time? After all, 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?
  • 31.  
  • 32. 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 .
  • 33. A loop prominence – lets us visualize the magnetic field.
  • 34.  
  • 35.  
  • 36. 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.
  • 37.  
  • 38. Sun spots
    • Where the loops of magnetic field penetrate the sun’s surface, they tend to cool it. The result is a darker, cooler area…a sunspot.
    • 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.
  • 39.  
  • 40.  
  • 41. Umbra & Penumbra
    • Just like the parts of the shadow of a solar eclipse, the darkest part of a sunspot is the umbra .
    • The surrounding, slightly less dark area is the penumbra .
  • 42.  
  • 43. Missions to the Sun
    • SOHO
    • Ulysses
    • Genesis
  • 44. SOHO
    • ( So lar and H eliospheric O bservatory) – a joint venture between ESA & NASA.
    • Looks continuously at the sun from a fixed spot in space.
    • Observes flares, CME’s & comets falling into the sun!
  • 45.  
  • 46. Ulysses – designed to orbit over the sun’s poles & provide a perspective that we can’t get from earth. This is ESA’s logo.
  • 47. Ulysses mission
  • 48. Genesis Mission
    • The Genesis mission was designed to orbit the sun and collect samples of the solar wind .
    • It returned these particles to Earth for examination.
    • Genesis orbited at a point called the L1 Lagrange point - a place in space where earth’s gravity exactly cancels the sun’s gravity.
  • 49.  

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