1. Chapter 14 Our Star

2. Radius: 6.9 x 108 m (109 times Earth) Mass: 2 x 1030 kg
(300,000 Earths)
Luminosity:
3.8 x 1026 watts
Good Sun movies to download:
Images compiled from Owen Gingerich’s copy of the first edition of Istoria e Dimostrazioni
Wave_fade.mpg photosphere:chromosphere:corona, optical:UV:X-ray
C2_1mth.mpg

3. What powers the sun?
The Sun's energy is produced by the thermonuclear process called hydrogen fusion
Small nuclei combine to form larger nuclei

4. Proton – Proton Reaction
The Sun releases energy by fusing four hydrogen nuclei into one helium nucleus. The overall reaction is:

5. Gravitational contraction:
Provided energy that heated core as Sun was forming
Contraction stopped when fusion began, which created outward pressure
Gravitational equilibrium:
Energy provided by fusion maintains the pressure that balances gravity

6. Solar Thermostat
Decline in core temperature causes fusion rate to drop, so core contracts and heats up
Rise in core temperature causes fusion rate to rise, so core expands and cools down

7. Radiation Zone:
Energy transported upward by photons

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

9. Photosphere:
Visible surface of Sun
~ 6,000 K

10. Surface has a speckled or honeycomb appearance called granulation.

11. Chromosphere:
Middle layer of solar atmosphere
~ K

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

13. How does the energy from fusion get out of the Sun?
Energy gradually leaks out of radiation zone in form of randomly bouncing photons.
Called the random walk.
Can take

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

15. Bright blobs on photosphere are where hot gas is flowing towards the surface. Dark areas are where gases are falling inward.

16. Solar Activity
Solar activity is associated with strong magnetic fields on the sun.

17. Solar wind - A flow of charged particles from the surface of the Sun

18. Sunspots
Are cooler than other parts of the Sun’s surface (4000 K)

19. Strong magnetic fields often connect sunspot pairs

20. Solar flares- bursts of X-rays and charged particles into space
Last only a few minutes

22. Solar prominences eruptions of clouds of hot gases that form huge arches high above the sun’s surface.
May last for several weeks to months.

23. Rare, solar tornado

24. Corona appears bright in X-ray photos in places where magnetic fields trap hot gas
Wave_fade.mpg photosphere:chromosphere:corona, optical:UV:X-ray

25. Coronal mass ejections send bursts of energetic charged particles out through the solar system

26. Number of sunspots rises and falls in 11-year cycle

27. Sunspot cycle has something to do with winding and twisting of Sun’s magnetic field