A vocabulary of landscape — a landscape of words
1133 entries
airglow
The permanent faint luminescence of the upper atmosphere — the reason the night sky is never fully dark even with no moon, no cities, and no starlight. It is chemiluminescence: sunlight tears apart oxygen and other molecules during the day, and those atoms release the stored energy as light hours later when they recombine, mostly in a layer around 90 to 100 kilometers up. Unlike aurora, it has no arcs or curtains. It is diffuse, all-sky, and present at every latitude, every night.
Etymology
A twentieth-century English compound, generally credited to the astronomers Otto Struve and Sydney Chapman around 1950. Lord Rayleigh called it permanent aurora, which is right about the persistence and wrong about the cause. Aurora is the solar wind hitting the magnetosphere. Airglow is chemistry, and it happens everywhere.
Notes
Green is the commonest color, from atomic oxygen at 558 nanometers; red comes from a higher layer, and sodium adds a yellow line. Astronauts photograph it as a thin band on the limb of the earth. Venus and Mars have it too.