Structure of the Sun
The Sun was born about 4.6 billion years ago, and has been shining over and nurturing us and all life on earth. The major difference between the Sun and the Earth or the moon is that it is entirely composed of high temperature gases. The Sun is structured with layers and the core, in particular, has the highest temperature and density, and generates the sources of light and heat by nuclear fusion. It takes hundreds of thousands of years before the energy generated in the core reaches the surface of the Sun, and the energy travels the distance between the Sun and the Earth (around 150 million km) to reach us.