It is pointed out that the time scale of energy transport in the Sun is the Kelvin–Helmholtz time scale, of order 3×107 years, roughly 100 times longer than the photon-diffusion time estimated by Mitalas and Sills (1992). The difference corresponds to a factor Ugas/Urad, the ratio of thermal energy density to radiation energy density. Thus the heat transport, even when mediated by photons, is slowed down by the large heat capacity of the star. A numerical example calculation is presented.
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