An Etymological Dictionary of Astronomy and Astrophysics

The interstellar matter outside condensed molecular clouds.
Diffuse interstellar medium consists of a hot intercloud medium, a warm intercloud medium, and a cold neutral medium with hydrogen atom densities n_H ~ 0.003, ~ 0.25, and ~ 40 cm^-3, and mean gas → kinetic temperatures T_k ~ 5 x 10⁵, ~ 10⁴, and 80 K, respectively.

See also: → diffuse; → interstellar; → medium.