The faint airglow emission that is detectable at night. Under moonless conditions it amounts to about half of the light from the sky (the remainder being starlight). The overall spectrum is highly complex, but the dominant components are the auroral green light from oxygen at 557.7 nm, the sodium D lines at 589.3 nm, and various hydroxyl bands. The principal emission occurs in specific layers of the ionosphere: most at 80–100 km, but some at 200–300 km. See also dayglow; twilight glow.
Subjects: Meteorology and Climatology.