Return to index Nuclear energy is the energy present in atoms and released in nuclear reactions. Nuclear reactions take place in stars including the sun. These reactions also take place in substances like Uranium and Plutonium. There are two main kinds of nuclear reactions, fission and fusion. In the sun and other stars, atoms of Hydrogen combine to form Helium, this is called fusion.
Fusion only takes place at very high temperatures and pressures.
When two atoms of Hydrogen combine to form one atom of Helium, some of their mass is converted into energy. This is nuclear energy. The nuclear reactions in the sun generate an enormous amount of energy. Some of this energy is converted into light energy and radiated out in all directions. Without this energy we would be in serious trouble.