"Every time you look up at the sky, every one of those points of light is a reminder that fusion power is extractable from hydrogen and other light elements,
and it is an everyday reality throughout the Milky Way Galaxy."
--- Carl Sagan, Spitzer Lecture, October 1991
For centuries, the way in which the sun and stars produce their energy remained a mystery. During the Twentieth Century, scientists discovered that they produce
their energy by the fusion process. Einstein's theory that mass can be converted into energy provided the basis for understanding fusion. This theory was
further explored by other physicists who discovered two practical methods for achieving this conversion.
A Galaxy of Fusion Reactors.
This picture shows the inner region of the m100 Galaxy in the Virgo Cluster, imaged with the Hubble Space Telescope Planetary Camera at full resolution.
(Courtesy of NASA)
One method is fission in which heavy atoms, such as uranium, are split, thus releasing the internal energy that holds the atom together. Fission energy is
now being used commercially in the United States to produce about 20% of the nation's electricity. The other method of transforming mass into energy is fusion
in which light atoms, such as those of hydrogen, are fused or joined.
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