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Our Sun – Our Star

Our Sun – Our Star. 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!!. Mass: 2 x 10 30 kg or 330,000 times Earth’s mass!!. Density: 1.41 g/cm 3. What planet has this same composition?.

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Our Sun – Our Star

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  1. Our Sun – Our Star

  2. Diameter: 1,400,000 km, 864,000 miles4.5 light-seconds 1,300,000Earths couldfit inside! 109 Earths would fit across the diameter of the sun!!

  3. Mass: 2 x 1030 kg or 330,000 timesEarth’s mass!! Density: 1.41g/cm3

  4. What planethas this samecomposition?

  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)

  6. 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!

  7. 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?

  8. That’s right – sunspots!

  9. The Sun’s Structure • 3 Interior Layers • The core produces the energy • The radiative zone • The convective zone • 3 Atmosphere Layers • Photosphere • Chromosphere • Corona

  10. 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). • all radiation produced is gamma ()

  11. Radiative Layer • Made of H, He gases. • Not hot enough for fusion to take place, but so hot that normally transparent gases have become opaque to light. • Photons of light produced by core bounce from one atom to another in a “random walk”, like a gigantic pinball game.

  12. 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.

  13. Convective Zone • Made of H, He gases…still hot enough to be opaque to light. • 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.

  14. The tops ofconvection cellscan be seennear the sunspots.They are calledgranules, orgranularity.

  15. The Photosphere • The innermost of the sun’s atmosphere layers. • H, He gas finally cools enough that it becomes transparent to light. • Our sunlight originates from this layer. This is the surface that we see. • Only 300 km thick.

  16. Actualcolor of photo- sphere … is slightly greenish.

  17. The Chromosphere • 2nd atmosphere layer. • Glows in red H- light (the red line from the level 3 level 2 electron transition in H atoms). • Tends to filter out the slightly greenish color of the photosphere, so we see yellow light from sun. • Several thousand kilometers thick.

  18. 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.

  19. Features on the Sun’s Surface • All features are produced by sun’s wacky magnetic field. • Prominences & flares. • Sunspots • Coronal Holes • Coronal Mass Ejections

  20. 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.

  21. 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?

  22. 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.

  23. A loop prominence – lets usvisualize the magnetic field.

  24. 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.

  25. 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.

  26. 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.

  27. 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.

  28. 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.

  29. Sometimes, the cycle quits! • During the period 1645 to 1715, very few sunspots were observed. We call this 70 year period the Maunder Minimum. • At the same time, European weather watchers recorded a mini ice age across Europe. Temperatures fell several degrees year round, and winter storms were worse than normal.

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