The N II 2143‐Å dayglow from Spacelab 1

During the Spacelab 1 shuttle mission (November 28 to December 7, 1983) spectral measurements were made in the ultraviolet which resolve the N+(5S) doublet at 2143 Å from the NO (1‐0) gamma band at 2148 Å in the upper thermosphere. The measured slant path surface brightness profile of the N+ feature is well explained by photodissociative ionization of N2 with a yield of 0.2. The intensity of the N+ feature relative to the NO (1‐0) gamma band is dependent on the conditions prevailing at the time and location of the measurement. For the near‐twilight mid‐latitude measurements made here, in the upper themosphere the N+(5S) feature would contribute 20% to 75% of a low spectral resolution NO measurement.