An Occultation Problem and Its Astrophysical Application

This paper is devoted to a determination of the dependence of the filling factor and its fluctuations on the number and geometrical sizes of structural elements of the radiating medium that occupy a spectrometer's observing aperture. The consequences of the results obtained in the interpretation of observed spatial fluctuations in the surface brightness of quiescent prominences in EUV lines are discussed. It is shown that the role of random variations in the filling factor is insignificant among the other factors producing brightness fluctuations for the regions of prominences having high and moderate packing of filaments. At the same time, this role may become important for rarefied and weakly radiating regions.