airglow

airglow faint diffuse illumination of the night sky originating in the upper atmosphere. The energy in the form of visible light is derived from the sun's ultraviolet light, which ionizes atoms and dissociates molecules at heights between 40 and 200 mi (64-322 km) above the earth's surface. When the fragments collide and recombine, some atoms and molecules are left with excess energy, which they release as light at characteristic wavelengths. Most prominent in the visible spectrum are the red and green light of oxygen and the yellow light of sodium. In southern and northern polar regions the airglow is often masked by the aurora (see aurora borealis ). Airglow hampers optical telescopic observations on earth by reducing the apparent contrast between stars and space.

airglow A weak background emission of light over the whole sky, resulting mainly from the excitation of atmospheric oxygen at an altitude of around 100 km by solar radiation; also known as nightglow. Airglow emissions vary with the time of day. Green oxygen emission at a wavelength of 557.7 nm predominates at night. Sodium and red oxygen emissions are prominent in the twilight airglow. Airglow is also produced during daylight, and is 1000 times as intense as at night.

air·glow / ˈe(ə)rˌglō/ • n. a glow in the night sky caused by radiation from the upper atmosphere.