The light produced and emitted by the Earth’s own atmosphere, excluding thermal radiation, aurorae, lightning and meteor trains. The spectrum of the airglow ranges from 100 nanometres to 22.5 micrometres. A major component is an emission line due to oxygen at 558 nanometres, which originates in a layer 30 to 40 kilometres thick at a typical height of 100 kilometres 60 miles. From space, the airglow appears as a ring of greenish light around the Earth.