Theoretical considerations regarding the altitude of the layer responsible for the nocturnal emission of the sodiumD-lines

The altitude of the layer responsible for the nocturnal emission of the D-lines is discussed theoretically. General arguments are used to show that if the luminosity originates directly from atmospheric sodium, its location must be far lower than is indicated by the recent observations of Barbier and Roach. Should these prove to be even approximately correct, some other source would apparently have to be invoked.