A one-dimensional model of thermospheric odd nitrogen chemistry is used to simulate simultaneous rocket measurements of NO, N(4S) and O(3P) at twilight. Good agreement between the observations and the model is obtained for the N(4S) densities above 100 km and for the NO densities above 130 km. Differences between the N(4S) profiles from the upleg nightglow and downleg twilight airglow measurements are consistent with the diurnal variation of N(4S) predicted by the theory. The model shows that with high thermospheric temperatures the diurnal variation of NO decreases, while the N(4S) diurnal variation increases. This behavior is attributed to the temperature sensitivity of the rate for the production of NO from N(4S) and O2. The model is used to predict the solar cycle dependence of the NO chemiluminescence.