An Etymological Dictionary of Astronomy and Astrophysics
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An → interstellar cloud in which hydrogen is completely dissociated and which is less dense and dusty than → molecular clouds. In diffuse interstellar clouds photoabsorption of the background → ultraviolet (UV) radiation field is an important dissociating and ionizing process. Typical densities and temperatures of diffuse clouds are 10² to 10³ cm^-3 and 20 to 100 K respectively. Because of modest extinctions (≤ 1 mag), → photodissociation processes are important in diffuse clouds preventing the formation of larger molecules.

→ diffuse; → interstellar; → cloud.

An aggregation of gas and dust in the → interstellar medium containing large quantities of atoms, molecules, and dust. There are several types of interstellar clouds, such as → diffuse interstellar clouds, → dark clouds, → molecular clouds.

→ diffuse; → cloud.

An → interstellar cloud that surrounds the → heliosphere.

→ local; → interstellar; → cloud.