Why does the sun glow?
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The fusion processes happening near the core of the sun cause energy to be given off in the form of photons (see “Physical and Theoretical Chemistry”). The photons given off in the core of the sun collide with other atoms, which absorb photons and, in turn, give off additional photons. This process repeats, potentially millions of times, before photons at the surface of the sun are emitted off into space.
As a side note, everything tends to emit radiation in this way, at least to an extent—it’s just that most things on Earth are not nearly as hot as the sun. Even your own body releases electromagnetic radiation, but the photons coming from your body are in the infrared region of the spectrum, so we cannot see them with our eyes. However, infrared cameras can use the photons given off by a person’s body to locate people (or animals) in this way.