Über das Auftreten der Natrium-D-Linien im Nachthimmelleuchten und im Nordlicht
In the course of investigations of the twilight-effect of the D-lines of sodium 14 spectra were photographed on March 1, 1941, showing the strong aurora on this evening. The spectra prove unambiguously that the twilight-effect occures completely undisturbed and independent of the aurora observed at the same time; i.e. the layers normally emitting the D-lines in the night-sky are not affected by the aurora. The auroral spectrum does not contain the D-lines. Thus the aurora took place above the layer emitting the D-lines in the night-sky. Occasional observations of the D-lines in auroras of higher layers indicate that in such cases the sodium was of extraterrestrial origin.