1 / 59

Chapter 8 T he Sun and Other Stars

Chapter 8 T he Sun and Other Stars. Radius: 6.9  10 8 m (109 times Earth) Mass: 2  10 30 kg (300,000 Earths) Luminosity: 3.8  10 26 watts. What is the Sun’s structure?. Insert TCP 6e Figure 14.3. Core: Energy generated by nuclear fusion ~ 15 million K.

otto
Télécharger la présentation

Chapter 8 T he Sun and Other Stars

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 8The Sun and Other Stars

  2. Radius: 6.9  108 m (109 times Earth) Mass: 2  1030 kg (300,000 Earths) Luminosity: 3.8  1026 watts

  3. What is the Sun’s structure? Insert TCP 6e Figure 14.3

  4. Core: Energy generated by nuclear fusion ~ 15 million K

  5. How does nuclear fusion occur in the Sun?

  6. Fission Big nucleus splits into smaller pieces. (Example: nuclear power plants) Fusion Small nuclei stick together to make a bigger one. (Example: the Sun, stars)

  7. High temperatures enable nuclear fusion to happen in the core.

  8. The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus.

  9. IN 4 protons OUT 4He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower.

  10. Radiation Zone: Energy transported upward by photons

  11. How does the energy from fusion get out of the Sun?

  12. Energy gradually leaks out of radiation zone in form of randomly bouncing photons.

  13. Convection Zone: Energy transported upward by rising hot gas

  14. Convection (rising hot gas) takes energy to surface.

  15. Bright blobs on photosphere show where hot gas is reaching the surface.

  16. Photosphere: Visible surface of Sun ~ 6000 K

  17. Chromosphere: Middle layer of solar atmosphere ~ 104–105 K

  18. Corona: Outermost layer of solar atmosphere ~1 million K

  19. Solar wind: A flow of charged particles from the surface of the Sun

  20. Gravitational equilibrium: Energy supplied by fusion maintains the pressure that balances the inward crush of gravity.

  21. Gravitational contraction: Provided the energy that heated the core as Sun was forming Contraction stopped when fusion began.

  22. How we know what is happening inside the Sun?

  23. We learn about the inside of the Sun by … • making mathematical models • observing solar vibrations • observing solar neutrinos

  24. Patterns of vibration on the surface tell us about what the Sun is like inside.

  25. What causes solar activity?

  26. Solar activity is like “weather”. • Sunspots • Solar flares • Solar prominences All these phenomena are related to magnetic fields.

  27. Sunspots Are cooler than other parts of the Sun’s surface (4000 K) Are regions with strong magnetic fields

  28. Loops of bright gas often connect sunspot pairs.

  29. Magnetic activity causes solar flares that send bursts of X rays and charged particles into space.

  30. Magnetic activity also causes solar prominences that erupt high above the Sun’s surface.

  31. The corona appears bright in X-ray photos in places where magnetic fields trap hot gas.

  32. Charged particles streaming from the Sun can disrupt electrical power grids and can disable communications satellites.

  33. Insert TCP 6e Figure 14.21a unannotated The number of sunspots rises and falls in an 11-year cycle.

  34. Properties of Other Stars • Luminosity • Surface Temperature • Mass

  35. How do we measure stellar luminosities?

  36. Luminosity: Amount of power a star radiates (energy per second = watts) Apparent brightness: Amount of starlight that reaches Earth (energy per second per square meter)

  37. The relationship between apparent brightness and luminosity depends on distance: Luminosity Brightness = 4 (distance)2 We can determine a star’s luminosity if we can measure its distance and apparent brightness: Luminosity = 4 (distance)2 (brightness)

  38. The amount of luminosity passing through each sphere is the same. Area of sphere: 4 (radius)2 Divide luminosity by area to get brightness.

  39. Most luminous stars: 106LSun Least luminous stars: 10–4LSun (LSun is luminosity of Sun)

  40. Apparent Magnitude • Greek astronomer, Hipparchus • Brightest stars were magnitude 1 • Faintest stars were magnitude 6 • Quantitatively redefined by modern scientists: • Difference of five “magnitude” = brightness ratio of 100 • Star Vega = magnitude of zero • Brightness in units of watts/m^2 • Logarithmic scale – mag 1 is 2.512 times mag 2

  41. Apparent Magnitude (concluded) • Sun -26.4 • Full Moon -12.92 • Venus (max) -4.89 • Mars (max) -2.91 • Mars (min) 1.84 • M31 (Andromeda Galaxy) 3.44 • Best naked eye 7-8 • 7x50 binoculars 9.5 • My telescope ?? 10-12 • Hubble telescope 31.5

  42. How do we measure stellar temperatures?

  43. Every object emits thermal radiation with a spectrum that depends on its temperature.

  44. Remembering Spectral Types (Hottest) O B A F G K M (Coolest) • Oh, Be A Fine Girl, Kiss Me • Only Boys Accepting Feminism Get Kissed Meaningfully

  45. Lines in a star’s spectrum correspond to a spectral type that reveals its temperature. (Hottest) O B A F G K M (Coolest)

  46. How do we measure stellar masses? Insert TCP 6e Figure 15.7 unannotated

  47. We measure mass using gravity. Direct mass measurements are possible only for stars in binary star systems. M1 and M2 are the masses of the two stars p = period a = average separation 42 G (M1 + M2) p2 = a3

  48. Most luminous stars: 106LSun Least luminous stars: 10–4LSun (LSun is luminosity of Sun)

  49. Most luminous stars: 106LSun Least luminous stars: 10–4LSun (LSun is luminosity of Sun)

  50. Three Major Star Groups • The Main Sequence • Most follow the surface temp – luminosity trend of red=cool and blues=hot • Generate energy by fusing hydrogen in cores • Giants and Supergiants • White Dwarfs

More Related