On the measurement of sodium dayglow emission by means of a Zeeman Photometer

Calculations are presented of the absorption of radiant energy by sodium vapor in a magnetic field. These calculations are related to the observations of sodium dayglow using a ‘Zeeman photometer’ and it is shown that the observations show a systematic error depending on the time of day at which an observation is made. The direction of the systematic error, in the case of the dayglow measurements of Blamont and Donahue, will be such that the deduced abundances of atmospheric sodium will be overestimates in summer and underestimates in winter. Examination of the data confirms the existence of these effects. A method of correcting for them has been developed, and revised abundance values have been obtained. The average daytime abundance is 14×109 atoms/cm2 with little seasonal variation. The ratio of day to twilight abundances is 2/1 in winter and 5/1 in summer.