Is the earth a perfect black body

black body

black body, black body, Blackbody emittersA body which is distinguished by the fact that it absorbs the entire incident energy of electromagnetic radiation regardless of the direction of incidence and polarization. Its properties are independent of the material and only defined by the temperature, its absorption capacity αν is for all frequencies ν constant one, i.e. αν = 1.

In contrast to the black body, the white or reflective body has an absorption capacity αν = 0, i.e. it cannot absorb any radiation. For a black body is the emission K equal to the radiation density J and stands over

with the energy density u in relationship. The emission of a non-blackbody with an absorbance value

however, is through the relationship


The energy density u is a function of frequency ν and the absolute temperature T and after the Vienna's law generally given by

The function f is not yet explicitly defined here. Only Max Planck succeeded in introducing the energy quantum hypothesis, the generally valid explicit derivation in the form of Planck's radiation formula.

The experimental arrangement that comes closest to the concept of the black body radiator is a cavity with a small outlet opening (cavity radiator), the walls of which are kept at a constant temperature. The radiation can escape through a small hole in one of the walls. This arrangement is shown in Fig. 1. Fig. 2 shows the spectral intensity distribution of a black body according to Planck's radiation formula.