Defines airglow as faint global luminescence caused by excitation and de-excitation of atmospheric species by solar radiation (p.8). It classifies airglow into dayglow, twilightglow, and nightglow (p.3) and explains key emitting species such as O, O₂, N, and OH (p.5). The lecture derives mechanisms for the 557.7 nm green line and 630.0 nm red line emissions, including production and loss processes