Spectroscopic measurement of sodium dayglow: Absence of a large diurnal variation

Measurements of the sodium dayglow were made with the Pepsios spectrometer at Fritz Peak Observatory, Colorado (40°N, 105°W), from July to November 1973. The average dayglow/twilight intensity ratio in October and November was 2.0 at noon and 1.8 at noon ±4 hours. These results are entirely consistent with solar flux changes due to absorption at twilight and to the daytime albedo contribution, and no diurnal variation of sodium is required. A Ring effect contribution at the D2 line was observed with little diurnal or seasonal variation apparent.