Blackbody as Universal Reference Thermometer

The analysis on Computational Blackbody Radiation identifies a blackbody by a radiation spectrum with all frequencies of the same brightness or light intensity,  thus sharing a common temperature (equidistribution), together with maximal high frequency cut-off (expressing Wien's displacement law).

This makes a blackbody into a universal thermometer which can be used to define the temperature of an arbitrary body with arbitrary absorption/emission characteristic, through radiative equilibrium with the blackbody by near-resonance.

This makes it possible to compare the temperatures of two different bodies with different absorption/emission spectra, and in particular infer radiative transfer of heat energy from hot to cold.

Viewing a blackbody as a reference thermometer may remove some of the mystery of the common notion of a blackbody as an empty cavity absorbing all incident radiation. This may help to understand that the equally mysterious greenhouse gas effect is non-existent.