Fusion is the nuclear reaction in which the light atoms align themselves with heaver. At the same time energy released.

Fusion is in the sun and stars the main of the source of energy.

The heavier nuclei production spent more energy than lighter.

In a fission reaction the heavier nuclei released energy when it dicomposing to the lighter nuclei.

The nuclei of atoms product from protons with a positive electric charge, and uncharged neutrons.

The positively charged nuclei between the affected electrical repulsio which prevents the grouping of nuclei in normal conditions.

When the substance is very hot, the nuclei moves so fast and the kinetic energy of their is so high that the electrical repulsion isn`t enough for prevents colisions of their.

The substance also should be sufficiently dense so that the small nuclei can hit each others.

Sun, like the other stars, produce energy from the fusion of hydrogen to helium.

Change the hydrogen into helium can happen in several routes.

The sun fuses 620 million tons of hydrogen each second.

The energy released only if a result of fusion is iron or lighter element nuclei.