Compare the theories that scientists proposed about the source of the sun's energy with the process of nuclear fusion in the sun

The sun's source of energy is know as nuclear fusion (means to fuse) this process has a small nuclei atoms that join together to form a large nucleus. The result of this process is released energy. The fusion of hydrogen into helium in the sun makes a large amount of energy and this is known as the sun's energy source.
The theories that scientist proposed about the source of the sun's energy was that the sun burned fuel to generate its energy and that gravity was causing the sun to shrink slowly and have its energy released. Also both of these theories were disproved.
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