The turbidity of the cloudless sky at Athens, Greece, is investigated by means of pyrheliometric measurements made with No. 116 Kipp-Zonen pyrheliometer at the National Observatory, Athens. The measurements are based on observations of the direct sun radiation using two filters (red and yellow) and without a filter. The monochromatic turbidity is defined and used to compare the atmospheric transmission at Athens with the theoretical value for a Rayleigh (molecular) atmosphere. The results give an indication of the unique clarity of atmosphere in the Attica area.
Research performed during author's stay at University of California, Los Angeles, Calif.