What is the difference between nuclear fission and nuclear fusion?

Webster's New World defines fusion as "melting together." Therefore, nuclear fusion is the process by which more than one nuclei join together to form a heavier nucleus. Nuclear fusion is the process that powers our sun and the stars. Nuclear fission is the exact opposite process, in which the nucleus of an atom splits into two or more smaller nuclei. As of today, fission is what produces the energy in nuclear power. Unlike fossil fuel energy sources like coal and gasoline, which produce tremendous air pollution that evidence suggests is depleting the earth's ozone layer, nuclear energy produces no air pollution. But the waste products of nuclear fission are highly radioactive and remain so for hundreds of years. At this time, a world-wide research program is underway to harness fusion energy to produce electricity, which would also create radioactive waste material but it would decay much more rapidly. The only by-product of nuclear fusion power would be Helium, a harmless gas. read less