effective temperature

Symbol T _eff, T _e. The surface temperature of a star, expressed as the temperature of a black body (i.e. a perfect radiator) having the same radius as the star and radiating the same total amount of energy (E) per unit area per second. A star is thus being considered a black body and its effective temperature is thus given by Stefan's law: T _eff ⁴ = E /σ = L /4πR ²

σ is Stefan's constant and L and R are the star's luminosity and radius. Although accurate determinations of effective temperature are difficult, each spectral type has a characteristic range of T _eff; the total range is from about 2500 to over 40 000 kelvin. The Sun's effective temperature is 5770 K. The effective temperature is the best measure of the actual temperature of the gas in a star's outer layers.

Radiation temperature, T _r, is equivalent to the effective temperature measured not over the whole spectral range but over a narrow portion of the spectrum, for example at visible wavelengths, which gives the optical temperature.

effective temperature

[ə¦fek·tiv ′tem·prə·chər] (astrophysics) A measure of the temperature of a star, deduced by means of the Stefan-Boltzmann law, from the total energy that is emitted per unit area. (meteorology) The temperature at which motionless, saturated air would induce, in a sedentary worker wearing ordinary indoor clothing, the same sensation of comfort as that induced by the actual conditions of temperature, humidity, and air movement. (statistical mechanics) That temperature which can be inserted in the Boltzmann distribution formula to describe the relative populations of two energy levels which may or may not be in thermal equilibrium.