According to Kirchhoff's law, when two objects are in thermal equilibrium, both objects have the same temperature and each object emits as much energy as it absorbs. Also, the energy absorbed at each wavelength is equal to the energy emitted at the same wavelength.
In the case of thermal steady state (like the sun and planet earth), each object maintains its different temperature but they also emit as much as the absorb. However, the energy absorbed at each wavelength is not equal to the energy emitted at the same wavelength.In fact, the incident spectrum and the emitted spectrum are very different. Why?
Kirchoff's law, which state the emissivity =absorptivity at the same wavelength is only applicable for thermal equilibrium situations but is not true for steady state situations, correct?