1. Chapter 10
Our Star

2. Hydrostatic Equilibrium or Gravitational Equilibrium
The outward pressure force balances the inward gravitational force everywhere inside the Sun.

3. Gravitational Equilibrium in the Sun.

4. The Sun’s Properties

6. The Sun's Atmosphere
Photosphere - "sphere of light", the visible surface of the Sun
Chromosphere - "sphere of color", visible during solar eclipses
Corona - the Sun's outermost atmosphere. The outflow of gas in this region is called the solar wind, which is protons and electrons that have escaped the Sun's gravity.

7. Transition Zones

8. Solar Spectrum

9. The Chromosphere

10. Solar Corona

11. Auroras are caused by the solar wind.
Solar wind is an outward flow of fast- moving charged particles (mostly protons & electrons)

14. The Basic Structure of the Sun

15. The Sun's Interior
Thermonuclear core - the central region of Sun where fusion takes place due to high temperatures and pressures.
Radiation zone - a region inside a star where energy is transported outward by the movement of photons (radiation).
Convection zone - a layer inside a star where energy is transported outward by means of heat flow through the gasses of the star (convection).

16. Solar Density and Temperature

17. What makes the Sun shine?
Thermonuclear fusion at the Sun's core is the source of the Sun's energy.
4 Hydrogen > Helium + Light
Atoms (fusion) Atom

22. Mass loss? 4  1 hydrogen = 6.693  10-27 kg
- 1 helium =  kg
Mass loss =  kg
The missing mass is converted to pure energy ( i.e. light ) By Einstein’s energy/mass equation.
E = mc2

23. What does this mean?
Mass can be transformed into light This occurs during fusion.
Light be transformed into matter This occurs in pair production.
These are results from Einstein’s theory of Special Relativity.

24. For one hydrogen-to-helium fusion event, E = 4.3 x 10-12 Joules
This is a tiny number by itself ,
but when multiplied by the vast number of hydrogen atoms undergoing fusion
and considering the rate of fusion in the Sun,
the total power released is equivalent to exploding 100 billion- 1 megaton H-bombs per second!
Our sunshine has a violent birth.

25. Helioseismology- Understanding the Sun’s Interior
Modes of vibration
Vibrations on the surface of the Sun can be detected by Doppler shifts
Falling Gas (Red)
Rising Gas (Blue)

26. The Neutrino Problem
Standard solar model is the generally accepted theory of solar energy production.
The model predicts that billions of neutrinos per second flow from the Sun.
Neutrinos react very little with ordinary matter so detecting them is difficult.
Neutrino telescopes indicate that only 1/3 of the neutrinos predicted by theory are “seen.”
Web

27. Solar Neutrino “Telescopes”
Solar Neutrino detector in South Dakota. Cl nuclei would turn into Ar nuclei when they captured solar neutrinos
Super –Kamiokande experiment in Japan is one of the world’s latest neutrino detectors.

29. Convection Transports Energy Outward
Cell

30. Granulation- Convection Cells in Photosphere

31. Sunspot Groups

32. Lines closer together represent stronger magnetic fields
Magnetic Field Lines
Lines closer together represent stronger magnetic fields
Charged particles spiral along field lines
Compass needles align with the magnetic field lines

33. Sunspot Pairs

34. Solar Prominence - a flame-like protrusion seen near the limb of the Sun and extending into the solar corona. These follow magnetic field lines.
Solar Flare – Huge and sudden release of energy on the solar surface, probably caused when energy stored in magnetic fields is suddenly released.

35. Solar Prominences – SOHO mission

36. Solar Flare –TRACE Mission

37. Sun in X-Ray
Corona

38. Sunspot Cycle
The rotation rate varies from once every 25 days to once every 30 days.
This differential rotation twists the magnetic field lines.
This causes the number of sunspots to vary over an 11 year period.

40. Solar Cycle
A 22 - year period that is needed for both the average number of spots and the Sun’s magnetic field polarity to repeat themselves. The Sun’s polarity reverses on each new 11-year sunspot cycle.

42. Magnetic Field lines become distorted due to the Sun’s Differential Rotation

44. Simmary of Surface Features
Granules - convection features about 1000 kilometers in diameter seen constantly in the solar photosphere.
Sunspot - a temporary cool region in the solar photosphere created by protruding magnetic fields.
Prominence - a flamelike protrusion seen near the limb of the Sun and extending into the solar corona.

45. Solar Telescope

47. The Sun Now

48. End of Section