Fusion is what powers the sun. ... Both fission and fusion are nuclear reactions that produce energy, but the applications are not the same. Fission is the splitting of a heavy, unstable nucleus into two lighter nuclei, and fusion is the process where two light nuclei combine together releasing vast amounts of energy.

Nuclear Fusion
Nuclear fusion is the process by which the sun produces energy. It is the merging of two atomic nuclei to form a heavier nucleus, releasing a large amount of energy in the process. This process occurs in the sun's core, where the temperature and pressure are extremely high.

Continuous Energy Emission
The sun emits energy continuously because nuclear fusion reactions are constantly occurring in its core. These reactions involve the fusion of hydrogen nuclei to form helium nuclei, releasing energy in the form of light and heat. This ongoing fusion process is what sustains the sun's energy output.

Comparison with Nuclear Fission
Unlike nuclear fission, which involves the splitting of atomic nuclei and is used in nuclear power plants on Earth, nuclear fusion is the primary source of energy production in the sun. Fusion reactions in the sun are more efficient and produce more energy compared to fission reactions.

Uninterrupted Energy Source
The sun's immense gravitational pressure and high temperature create the conditions necessary for nuclear fusion to occur continuously. As long as there is a sufficient supply of hydrogen fuel in the sun's core, the fusion reactions will continue, resulting in the sun's steady emission of energy.
In conclusion, the continuous emission of energy by the sun is due to the process of nuclear fusion occurring in its core. This natural phenomenon sustains the sun's energy output and provides heat and light to support life on Earth.