Höhenbestimmung der in der Dämmerung leuchtenden atmosphärischen Natriumschicht

This paper reports on observations of the D-lines of sodium in the twilight made at Braunschweig in 1941. The sudden decrease of intensity of the sodium lines in the evening twilight and the sudden enhancement in the morning twilight was photographed in short intervals with a spectograph of high aperture in two directions (zenith and horizon). The evaluations of the spectra show that the D-lines must be excited by ultraviolet light of the sun, for which the ozone-layer of the upper atmosphere is not transparent. The upper limit of this screening ozone layer was determined to 54 ± 3 km. The sodium layer shows also a sharp upper limit at 118 ± 2,5 km. Occasional observations show a not well defined under limit of the sodium layer at 106,5 ± 6 km corresponding to a thickness of 11,5 ± 6,5km for the light-emitting sodium layer. The possible errors are discussed thorougbly. The obtained values are in good agreement with reults of other authors.