Why do stars shine?
Quick Answer
Stars shine because nuclear fusion in their cores converts mass into energy. In the Sun, hydrogen nuclei fuse into helium under extreme temperature and pressure.
The Full Story
A star is powered by the balance between gravity pulling inward and pressure from nuclear reactions pushing outward. In the Sun’s core, temperatures reach about 15 million°C, allowing hydrogen nuclei to fuse through the proton-proton chain. That fusion converts a small amount of mass into a huge amount of energy, described by Einstein’s E = mc². The energy eventually reaches the surface as light and heat, which is why the Sun shines. This same basic process powers most stars, though more massive stars can also use the carbon-nitrogen-oxygen cycle.
Key Facts
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