Why does the sun shine?

To a large extent, the sun is made up of hydrogen, which is converted into the element helium inside the sun's atmosphere. In the resultant fusion of two hydrogen atoms with helium, a lot of energy is released. As a result, the core of the sun heats up to an unimaginable
temperature: about 8 million °C! On the surface of the sun, the temperature is 'only' around 550o °C. 

The sun releases this heat energy in the form of radiation, which gives it its fiery glow. About every 11 years, the
surface of the sun changes and what we know as sunspots occur. The surface is somewhat cooler and darker around the spots. Thus, they radiate less energy. A few researchers believe that an increase in the occurrence of these spots causes ice ages on the Earth.