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

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.

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.

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?

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

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)

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.

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.

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.

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.

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.

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.

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

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?

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.

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).

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.

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.