Spectra of the night sky gathered as a by-product of astronomical observations made at two Keck telescopes at Mauna Kea, Hawaii are used to improve our understanding of chemistry and composition in the upper mesosphere and thermosphere. The data acquisition has recently expanded to include similar spectrographic data from the European Southern Observatory in Chile, and from the 9-meter telescope at McDonald Observatory in Texas. The use of the data for aeronomy focuses on three discoveries made in a preceding research effort. First, a ratio of the sodium D1 to D2 emission intensity is found to have a surprising semiannual oscillation, which preliminary investigation indicates is modulated by the O:O2 number density ratio in the upper mesosphere. This research attempts to prove that hypothesis, and thereby establish an unprecedented proxy for determining the density of the dominant species in the upper atmosphere - a long standing and elusive target for ground-based aeronomy. The second research task investigates the ratio of the O(1D):N(2D) ratio (the latter a unique measurement capability of these large telescopes) relative to model values that currently do not reproduce the data. The third research task uses the heretofore unappreciated detail of the OI Rydberg series to peg ratios that can be used for instrument sensitivity calibration throughout the airglow observation community - and thereby improve density determinations made from airglow data.
