BRAINCAKEStefan's Law
The luminosity L of a star is the total radiant power it emits, in watts. The Stefan-Boltzmann law (Stefan's law) gives the luminosity of a black body:
L = 4πr2σT4
where r is the radius of the star, T is its surface temperature in kelvin, and σ is the Stefan constant, 5.67 × 10−8 W m−2 K−4. The term 4πr2 is the star's surface area, so σT4 is the power emitted per square metre of surface.
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