General Astronomy/Convective and Radiative Zones

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The Sun is composed of a number of zones in which energy is produced or transported to the surface. The nuclear process of fusion occurs in the core, and radiation is transported from there to the surface, undergoing numerous transformations into longer wavelength radiation, ultimately ending up on the surface as mostly visible wavelength light that immediately flies away at the speed of light.

Directly above the Sun's nuclear fires in the core is a large zone called the radiative zone or radiation zone in which energy moves primarily in the form of high energy photons. Nearer the surface the photons are largely absorbed by the material in the Sun, heating it up. Energy transport from this point is primarily via convection, or the physical movement of the hotter material upward to areas of lower temperature and pressure, like water boiling in a pot. This is the convective zone or convection zone.

At the top of the convection zone is the photosphere, the region at which much of the transported energy converts back into visible light to be radiated into space.