Energy Flow in Stars

The Sun produces aboutof power. This energy is produced by nuclear fusion of hydrogen to helium in the core, the reaction being

The core has to be at a very high temperature for this to happen. The Sun's core is at a temperature of almost 15 million degrees Kelvin.

The mass of the products is less than the mass of the reactants, and the difference m is released as energy in the form of kinetic energy and electromagnetic radiation according toThis energy moves outwards from the core, partly through convection and partly through radiation. As it moves outwards it cools – so that particles move less fast, having less kinetic energy, and electromagnetic radiation has a longer wavelength. The Sun is losing mass in this way at the rate of

By the time the energy reaches the surface of the sun the temperature is only around 6000 degrees Kelvin. At the surface, the energy is released mostly through electromagnetic radiation, but also through a stream of particles called the solar wind.