The Universe
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16. Star Power
Figure 10.11 Nuclear fusion


The Sun is Earth’s major source of energy, yet the planet only receives a small portion of its energy. The Sun is just an ordinary star.


Many stars produce much more energy than the Sun. The energy source for all stars is nuclear fusion.

Nuclear Fusion

Stars are made mostly of hydrogen and helium, which are packed so densely in a star that in the star’s centre the pressure is great enough to initiate nuclear fusion reactions.

In a nuclear fusion reaction, the nuclei of two atoms combine to create a new atom.

Most commonly, in the core of a star, two hydrogen atoms fuse to become a helium atom.

Although nuclear fusion reactions require a lot of energy to get started, once they are going, they produce enormous amounts of energy

The reaction is presented like this

2 H → He + Energy

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