tomorrow's energy supply
Source: NASA Goddard Space Flight Center [CC BY 2.0], via Wikimedia Commons
Nuclei of lighter atoms such as hydrogen collide and fuse together to produce nuclei of heavier atoms such as helium and release vast amounts of energy in the process —this is the essence of fusion. Because the energy is derived from the action of nuclei, fusion is a form of nuclear energy. It maybe considered the opposite of fission, also a form of nuclear energy, which is generated when nuclei of heavy atoms into split into lighter ones. Fusion is the process that powers and drives the production of energy in stars, such as our Sun.
Some 70 years ago scientists obtained the first insights into the physics of sunshine: when the sun and other stars transmute matter, tirelessly transforming hydrogen into helium by the process of fusion, they release colossal amounts of energy.