Who discovered the relationship between a star's temperature and it's brightnesss?

Answer 1

The Stefan-Boltzmann law, also known as Stefan's law, states that the total energy radiated per unit surface area of a black body in unit time (known variously as the black-body irradiance, energy flux density, radiant flux, or the emissive power),J is directly proportional to the fourth power of the black body's thermodynamic temperature T (also called absolute temperature):
J=sigma*T^4
where sigma= stefan-boltzmann constant= 5.6705*10`-8 W/m2K4