Nuclear fusion occurs within the sun and the stars. Fusion in the sun is believed to occur in steps. Four protons produce one atom, two positrons, and two neutrinos. Sunlight is energy released from fusion reactions in the sun. Examining the spectral characteristics of stars may provide a better understanding of fusion.
Fusion is believed to be possible only under extremely high temperatures.
For this reason it is referred to as a thermonuclear reaction. The use of nuclear fusion for commercial purposes is currently being investigated. The fuel needed for fusion is readily available. Deuterium must be extracted from water. It is also toxic.