1. Earth Science 24.3B The Sun’s Interior The Solar Interior

2. Earth Science 24.3 The Sun The Solar Interior:  The interior of the sun can not be observed directly.  For that reason, all that we know about it is based on information acquired from the energy it radiates and from theoretical studies.

3. Earth Science 24.3 The Sun Nuclear Fusion:  Deep in it’s interior, the sun produces energy by a process known as nuclear fusion.  This nuclear reaction converts four hydrogen nuclei into the nucleus of a helium atom.

4. Earth Science 24.3 The Sun  During nuclear fusion, energy is released because some matter is actually converted to energy.  How does the process of nuclear fusion work?

5. Earth Science 24.3 The Sun  Consider the four hydrogen atoms have a combined atomic mass of 4.032 atomic mass units ( 4 X 1.008) whereas the atomic mass of helium is 4.003 atomic mass units. ( a difference of 0.029 units)  This tiny difference is emitted as energy according to Einstein’s equation ( E = mc 2 ).

6. Earth Science 24.3 The Sun  According to Einstein’s equation, seen at right, E equals energy, m equals the mass, and c equals the speed of light. E = energy M = mass C = speed of light (300,000 mp/s)

7. Earth Science 24.3 The Sun  Because the speed of light (c) is great (300,000 kilometers per second), the amount of energy released from even a small amount of material is enormous.  The hydrogen bomb the United States military developed was made possible by creating such a reaction.

8. Earth Science 24.3 The Sun  The conversion of just one pinheads worth of hydrogen to helium generates more energy than burning thousands of tons of coal.  Most of this energy is in the form of high-energy photons that work their way toward the solar surface.  The photons are absorbed and reemitted many times until they reach a layer just below the photosphere.

9. Earth Science 24.3 The Sun  Here, convection currents help transport this energy to the solar surface, where it radiates through the transparent chromosphere and corona.  Only a small percentage of the hydrogen in the nuclear reaction is actually converted to energy.

10. Earth Science 24.3 The Sun  Nevertheless, the sun is consuming 600 million tons of hydrogen each second; about 4 million tons are converted to energy.  As hydrogen is consumed, the product of this reaction, helium, forms the solar core, which continually grows in size.

11. Earth Science 24.3 The Sun  Just how long can the sun produce energy at it’s present rate before all of it’s hydrogen fuel is consumed?  Even at the enormous rate of consumption, the sun, has enough fuel to last easily for another 100 billion years.

12. Earth Science 24.3 The Sun  However, evidence from observing other stars indicates that the sun will grow dramatically and engulf the Earth long before all of it’s hydrogen is gone.  It is thought that a star the size of the sun can exist in it’s present stable state for 10 billion years.

13. Earth Science 24.3 The Sun  As the sun is already 4.5 billion years old, it is “middle aged” at present.

14. Earth Science 24.3 The Sun  For fusion to occur however, the sun’s internal temperature must have reached several million degrees.  What caused this increase in temperature?

15. Earth Science 24.3 The Sun  The solar system is believed to have formed from an enormous compressed cloud of dust and gases, mostly hydrogen.  When gases are compressed, their temperature increases due to the higher pressure they are under.

16. Earth Science 24.3 The Sun  All of the bodies in our solar system are compressed.  The sun however, because of it’s enormous size, was the only object to become hot enough for nuclear fusion to occur.  Astronomers currently calculate it’s internal temperature at 15 million degrees Kelvin (K).

17. Earth Science 24.3 The Sun  The planet Jupiter is basically a hydrogen-rich ball as well.  If it were about 10 times more massive, it too would have converted into a star capable of nuclear fusion.

18. Earth Science 24.3 The Sun  The idea of one star orbiting another seems odd but recent evidence indicates that about 50 percent of the stars in the universe occur in pairs or multiple stars within a single system.