Clear sky emissivity as a function of the zenith direction

Using the Bliss's theory [1] which assimilates the atmosphere as a column constituted of plane and parallel layers, the expression of the clear sky emissivity as a function of the zenithal direction is established. Other relations as the mean emissivity and the temperature of a part of the celestial vault are also established. The power emitted by some parts of the sky are calculated. Experiments have been conducted. This paper describes the study and presents the results.