Propagation of an artificial lighting in the atmosphere

Abstract

The work discussed the problem of propagation of light originating from ground light sources. Such light impacts on the environment both directly as well as indirectly by dispersing on the atmospheric aerosols, contributing to the so-called artificial airglow. Such effect is especially important in the case of protected areas located in the vicinity of human settlements, which are the strong sources of light pollution. Extinction of light in the atmosphere, as well as terrain or vegetation causes that at a distance just a few kilometres from light source its direct impact on the environment is negligible. In case of an artificial airglow, the situation is more complex. The analysis of the measurement data collected within a few years has shown that artificial airglow is ecologically important only in the case of overcast sky and that the important factor is the cloud base. It seems that with the low clouds this effect is practically limited to the part of celestial sphere located directly above the light source and disappears very quickly with increasing distance. In case of a cloudless sky or with high clouds, the area of the lighted part of the sky is growing, but the contribution of light pollution in its surface brightness decreases significantly. This means that while the artificial airglow of the cloudless sky is an important problem in astronomical observations, it has a rather negligible ecological impact. The described analysis points to the need of protection of the near vicinity of protected areas first of all from defectively constructed ground lighting. It also indicates the possibility of preserving ecologically dark sky even in the vicinity of large urban centres. At the same time it confirms the necessity of location of astronomical observatories away from any human settlements.