The sun is about 864000 miles wide and filled with sweltering hot gases. Hydrogen is the most abundant element present in the Sun, composition of the Sun by its constituent mass is 71% hydrogen (H), 27% helium (He) and 2% other heavier elements. Inside the Sun the gravitational pull compresses the gases, and increase the temperature and pressure at the core. (CAIN, F., 2009) The temperature is about 10000°F on the surface and more than 28 million degrees Fahrenheit at the core of the sun. The pressure at the core of the sun is 250 billion times the pressure at earth`s surface. Due to the extreme condition at the sun`s core, neither the Hydrogen molecules (H2) nor the Hydrogen atoms (H) can remain stable, and the orbital electron of the hydrogen atoms get separated from its atomic structure. Separation of the negatively charged orbital electron, results in complete ionisation of the gas with a positively charged proton at the hydrogen nucleus.
The gravitational force at the solar core try to squeeze the Sun but, it simultaneously creates an ideal condition for the ionized hydrogen to initiate nuclear fusion by increasing temperature and pressure. The positively charged proton of hydrogen nuclei move at very high speed and overcome their electrical repulsive force to collide, and fuse with each other. The fusion of hydrogen nuclei initiate a chain reaction at the sun`s core that finally converts the hydrogen into helium and generates enormous energy. The entire process of fusion between the protons of hydrogen nuclei, and subsequent generation of helium and energy is known as nuclear fusion or proton-proton (p-p) chain reaction. (BAHCALL, J., 2001).
The nuclear burning begins with the fusion of two hydrogen nuclei (¹H) and produces a heavy hydrogen nucleus (²H, deuteron), a positively charged electron (positron, e+) and energy (ᵞ).
¹H + ¹H→ ²H + e+ + energy
In the next step the deuterons (²H) fuse with a proton and produce light nuclei of helium (³He) and energy.
²H + ¹H → ³He + energy
Finally the two ³He collide and fuse into a single helium nucleus (⁴He), two positrons (e+), two neutrinos (ᵞ), and energy.
³He + ³He →⁴He + 2 e+ + 2ᵞ + energy
Neutrinos (ᵞ) are the subatomic particles that interact very weakly with matter and travels at the speed of light.
Nuclear fusion converts a small mass into an enormous amount of energy in accordance with Einstein’s equation E=mc². Where E=energy, m=mass, and c=speed of light (3×10¹° cm/sec.). The fusion generated energy at the core of the Sun is electromagnetic radiation, and mostly in the form of gamma rays of short wavelength. The energy generated from hydrogen fusion heats up the solar core as well as heats up the other solar layers on their way to the surface of the Sun.
Based on the Sun`s luminosity and the energy released per proton-proton chain reaction the number of nuclear fusion reactions taking place at the solar core in every second is calculated as 9× 10³⁷("Fusion Chemistry - A Closer Look.")
The convection zone has much less temperature than its inner solar region and the gas atoms can retain their undamaged atomic structure. The gas atoms absorb the energy of visible light and become severely hot. At the lower level of convection zone, the increase in temperature raises the gaseous volume, and the heated gas move up to the surface of convection zone. At the surface of convection layer the boiling motion of gases radiate away the excess heat, and cool down. The gases become heavier as they cool off, and again return to the bottom of convection layer. The hot bundles of gas continue to collect heat from the bottom and radiate off the heat at the surface of convection layer in a cyclic manner like convection current.
Above the convection layer the consecutive three regions of the sun`s surface are photosphere, chromospheres, and solar corona. The photosphere is the immediate region after the convection layer and it is the bright visible surface of the Sun and the lowest layer of solar atmosphere. The photosphere is one of the coolest regions of the Sun and in this region the gases are also stable with their atomic structure and have less density than in the convection layer. The gaseous atoms radiate the excess energy from the photosphere and streams of energy travel through the space and finally reach at the earth`s surface.
The electromagnetic waves released from the solar photosphere are radiated in every direction and reaches to the earth as a wide range of wavelengths. The wavelengths of the electromagnetic waves vary from infrared (IR) to ultraviolet (UV) region and between theses region the waves include the visible spectrum. When the solar electromagnetic radiation reaches the earth some of the radiations enter into the surface of earth and heats up the atmosphere, whereas some radiations like ultraviolet rays are absorbed in the ozone layer and radiated back.
So, the gamma rays produced from the hydrogen fusion are the combined energy source of visible light and heat of the Sun because, in the process of hydrogen fusion, the produced energy heats up the constituent particles at the solar core, and then transfer the energy in different layers as they move up to the surface, finally the energy generated as gamma rays is transformed and split in infrared, visible light spectrum and ultraviolet rays, and escapes from photosphere to reach the earth.
The Sun produces heat and light from the hydrogen fusion.
Reference:
BAHCALL, J. (2001). How the Sun shines. Retrieved November 21, 2014, from http://www.slac.stanford.edu/pubs/beamline/31/1/31-1-bahcall.pdf.
CAIN, F. (2009, October 7). Why is the Sun Hot? Retrieved November 20, 2014, from http://www.universetoday.com/42270/why-is-the-sun-hot/.
"Fusion Chemistry - A Closer Look." SCIENCE. NASA. Web. 19 Nov. 2014. http://genesismission.jpl.nasa.gov/science/mod3_SunlightSolarHeat/FusionChemistry/.
"Solar Structure - A Closer Look." SCIENCE. NASA. Web. 20 Nov. 2014. http://genesismission.jpl.nasa.gov/science/mod3_SunlightSolarHeat/SolarStructure/index.html
