An Etymological Dictionary of Astronomy and Astrophysics
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A medium in which several molecular clouds are situated.

→ inter- + → cloud + → medium.

A component of the → interstellar medium consisting of an extremely tenuous (density 0.1 to 10 cm^-3) and relatively warm gas (temperature about 8,000 K) filling the space between denser neutral and ionized gas. Hydrogen is partly ionized, partly atomic and observed by the → 21-centimeter line in emission.

→ warm; → intercloud medium.