Flexi Says: Although people sometimes say that the Sun is "burning," this term is not an accurate description of the reaction that produces the Sun's light and heat. Burning is a chemical reaction in which oxygen rapidly reacts with a hydrocarbon fuel like gas or wood and releases a relatively small amount of energy. Chemical reactions involve only the electrons of atoms. No new atoms are formed in chemical reactions, they are only rearranged into different compounds. Stars like our Sun are powered instead by nuclear reactions. Nuclear reactions involve the nuclei of atoms, which contain protons and neutrons. New elements can be formed in nuclear reactions. Nuclear fusion occurs in the core of our Sun and other stars. In this process, hydrogen fuses into helium and a vast amount of energy is released.