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Nuclear reactions are processes where the nucleus of an atom changes its structure. These changes involve a tremendous amount of energy because the bonds holding the nuclei together are extremely strong.
Unlike chemical reactions, which involve electrons and result in relatively small energy changes, nuclear reactions release much more energy.
This energy release can be several million times greater than that of chemical reactions.
In nuclear reactions, atoms can either split (fission) or combine (fusion).
Fission splits a heavy nucleus into smaller nuclei, while fusion combines light nuclei into a heavier one.
The type of nuclear reaction at work in the sun is fusion.

The sun produces energy through nuclear fusion reactions in its core. The core is extremely hot and dense, providing the right conditions for hydrogen nuclei to collide and fuse.
In the sun, hydrogen atoms combine to form helium, and in the process, they release a massive amount of energy.
This energy then travels from the core to the sun’s surface and radiates into space.
Scientists estimate that the sun converts approximately 600 million tons of hydrogen into helium every second.
This process not only produces light and heat but also powers the entire solar system by emitting energy across various wavelengths.
The sun’s energy supports life on Earth and drives weather, climate, and biological processes.

Fusion reactions involve the merging of two light atomic nuclei to form a heavier nucleus, which releases energy.
In the sun, this primarily involves the fusion of hydrogen nuclei (protons) to form helium.
This process can be summarized in several key steps:

• Two protons fuse to form a deuterium nucleus, releasing a positron and a neutrino.
• The deuterium nucleus fuses with another proton to form helium-3.
• Two helium-3 nuclei then combine to form helium-4, releasing two protons.

These fusion reactions occur under conditions of extreme temperature (millions of degrees) and pressure.
The energy released during these reactions is what we see as the sun’s light and feel as its heat.
Unlike fission, which splits heavy elements like uranium, fusion combines lightweight elements like hydrogen and is the source of energy for stars, including our sun.