The extent to which the Earth's atmosphere transmits light from celestial objects. The atmosphere's clarity varies widely, depending on the amount of absorbing material such as water vapour, dust, aerosols (suspended fine particles), and polluting gases. In general, transparency improves with altitude, particularly above inversion layers, which occur where cold surface conditions produce a layer of cold air close to the ground which traps much of the absorbing material. In temperate latitudes, transparent air often follows a cold front. See also atmospheric extinction.
Subjects: Astronomy and Astrophysics.