The fusion of atomic nuclei, resulting in the release of energy. Fusion energy is the basis for the radiation of stars, including the Sun. The process requires a temperature of over 10 million degrees, and extremely high pressure. Continuous fusion is possible only if the elements taking part are completely ionized into plasma.
In the fusion reaction inside a star, 4 hydrogen nuclei fuse into helium in the so-called proton-proton reaction, with the result that 0.7 percent of the star's mass during a star's main sequence phase turns into energy. Later, when the hydrogen reserves are exhausted, the star shrinks and at the same time heats up. Then the helium's nuclear reactions begin, and the star expands into a giant. Three helium atoms fuse into one carbon atom and once again energy is released.
The capacity of the Sun is c. 4 x 1026 watts. Calculations show that the Sun loses 4 million tons of its mass each second.
