Vacuum ultraviolet spectra of the late twilight airglow.

Evaluation of sounding rocket spectra of the late twilight (solar-zenith angle of 120 deg) ultraviolet airglow between 1260 and 1900 A. The only observed features are O I 1304 and 1356. When the instrument looked at an elevation of 17 deg above the western horizon, the brightnesses were 70 and 33 rayleighs, respectively. The upper limits on the total intensity of the Lyman-Birge-Hopfield and Vegard-Kaplan systems of N2 were 26 plus or minus 26 and 55 plus or minus 55 rayleighs, respectively. An estimate shows that a large part of the O I emissions may be due to excitation by conjugate-point electrons.