Effective Temperature

Definition

The effective temperature of a star is the temperature of a Black Body of the same size as the star and that would radiate the same total amount of electromagnetic power as emitted by the star.

Overview

Noted T_eff, the effective temperature is one of the fundamental parameters that characterizes a star. If P_* is the power radiated by a star of radius R, then T_eff is derived by applying the Stefan–Boltzmann law: P_* = 4 π R² σ T ⁴_eff . Indeed a star is not actually a black body, as its Emissivity varies with wavelength; however, the effective temperature generally provides a fair approximation of the actual temperature of the stellar photosphere. This is so because at any wavelength, the radiation comes from a more or less deep layer but which is always on the skinof the star and thus, at approximately a constant temperature. The effective temperature is directly related to the color of the star: the higher the temperature, the bluer the light emitted by the star. The...