Stefan-Boltzmann constant

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The Stefan-Boltzmann constant (also Stefan's constant), a physical constant denoted by the Greek letter σ, is the constant of proportionality in the Stefan-Boltzmann law: the total energy radiated per unit surface area of a black body in unit time is proportional to the fourth power of the thermodynamic temperature.

The value of σ is 5.670 400(40)×10−8 W·m-2·K-4. This value is derivable as well as experimentally determinable; see Stefan-Boltzmann law.

σ can be defined in terms of the Boltzmann constant kB as:

\sigma = \frac{2\pi^5k_{\mathrm B}^4}{15h^3c^2} = \frac{\pi^2k_{\mathrm B}^4}{60\hbar^3c^2},

where h is Planck's constant, \hbar = h/2\piis Dirac's form of Planck's constant, and c is the speed of light in a vacuum.

A related constant is the radiation constant ([1]) which is equal to

\frac{4\sigma}{c}.

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