Vacuum ultraviolet spectra of the late twilight airglow

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