## blackbody
A blackbody absorbs all the radiation that falls on it, converts it into internal energy (heat), and then re-radiates this energy into the surroundings. The re-radiated thermal energy, known as blackbody radiation, has a continuous
spectrum governed solely by the body's temperature.
For any given temperature, there is a specific wavelength at which radiation emission is greatest (see diagram labeled "Variation in blackbody curves with temperature"). The effective temperature (T_{e}), or blackbody
temperature, is the surface temperature that an object, such as
a star, would have if it were a blackbody that radiated the same amount
of energy per unit area. This is a useful and widely employed measure of
stellar surface temperature. T_{e} can be calculated from
the Stefan-Boltzmann law, which states that the total energy
radiated by a blackbody varies as the fourth power of its absolute temperature.
This law leads to the formula: L = 4σR^{2}T_{e}^{4}
where L is the luminosity of the
body, R is its radius, and σ (= 5.67 × 10^{-8}
W/m^{2}/K^{4}) is the Stefan-Boltzmann constant. (A simplified
form appears in the box on blackbody radiation laws below.) Substituting solar values for L and R gives a value for the
effective temperature of the Sun of about 5,780 K. ## Related category• HEAT AND THERMODYNAMICS | ||||||||||

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