The title of this article is ambiguous. For further meanings see effective temperature

Spectral radiation density of our sun (effective temperature around 5780 K ) compared to that of a black body of the same size (labeling in English)

The effective temperature of a star is the temperature of its surface that a black body would have to have in order to shine with the same brightness per area . The effective temperature of an object deviates from the kinetically defined temperature, the less the spectrum of the object corresponds to that of a black body.
${\ displaystyle T _ {\ mathrm {eff}}}$${\ displaystyle {\ mathcal {F}} _ {\ mathrm {Bol}}}$

${\ displaystyle {\ begin {alignedat} {2} L & = {\ frac {L} {A}} && \ cdot A \\ & = \ sigma T _ {\ mathrm {eff}} ^ {4} && \ cdot 4 \ pi R ^ {2} \ end {alignedat}}}$

With

the star's surface , where is the radius of the star.${\ displaystyle 4 \ pi R ^ {2}}$${\ displaystyle R}$

Since the stellar radius cannot be clearly defined, the optical density is used to calculate the effective temperature
.

The effective temperature and the bolometric brightness are the two physical parameters with which a star can be classified in the Hertzsprung-Russell diagram .