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A Greek sigma, relating temperature to radiated power.
Also known as: Stefan constant, Black-body sigma constant, Black body constant
σ converts a body's temperature to the power it radiates, and the relationship is to the fourth power — so doubling an object's absolute temperature multiplies its radiated power by sixteen. It is exactly derivable from the Planck and Boltzmann constants, so it is not independent.
Denotes the Stefan–Boltzmann constant, the proportionality between a black body's radiated power per unit area and the fourth power of its temperature.
Contexts: Laboratory
Is derived rather than measured: it is fixed exactly by the defined values of the Planck, Boltzmann and elementary-charge constants in the current SI.
Contexts: Laboratory
Collides with the Greek sigma used for electrical conductivity, surface charge density and standard deviation.
Contexts: Laboratory
A Greek lowercase sigma, a small loop with a horizontal stroke leading right from its top.