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 [′er‚glō]

(geophysics)

The quasi-steady radiant emission from the upper atmosphere over middle and low latitudes, as distinguished from the sporadic emission of auroras which occur over high latitudes. Also known as light-of-the-night-sky; night-sky light; night-sky luminescence; permanent aurora.

---

Airglow 

the luminescence of gases found in the upper atmosphere at altitudes above 70–80 kilometers; an important component of the luminescence of the night sky.

Airglow exhibits not only a continuous spectrum but also atomic emission lines of oxygen, hydrogen, and sodium and molecular bands of the hydroxyl radical, oxygen, carbon dioxide, ozone, water, and nitrogen oxides. The emission of the individual components of airglow occurs at various altitudes in strata of varying thickness. The altitude and thickness of the layers may change. One of the main energy sources for airglow is the energy of solar radiation, which causes dissociation and ionization in the upper atmosphere; the subsequent recombination of particles produces airglow.

The intensity of all the emissions depends on the degree to which the upper atmosphere is illuminated, on the density, temperature, and composition of the upper atmosphere at the altitudes where the emissions occur, on solar and geomagnetic activity, and on the latitude of the observation site. There are daily and seasonal cycles.

The mechanisms responsible for airglow have not yet been fully explained. Observations of the spectra of airglow and of variations in its intensity dependent on heliogeophysical conditions are widely used to obtain data on the composition, density, temperature, and other properties of the atmosphere at high altitudes.

REFERENCE

Chamberlain, J. Fizika poliarnykh siianii i izlucheniia atmosfery. Moscow, 1963. (Translated from English.)

IU. L. TRUTTSE