Stefan-boltzmann Law

Law of blackbody radiation that states that the amount of energy given off by a blackbody per second per unit area (flux) is proportional to the fourth power of the temperature of the blackbody. For flux (power per area)
expressed as J/m2s with σ = 5.6703 x 10-8 W/m2K4:

If R is the radius of a star, its luminosity is: