Gas (interstellar)
Diffuse atoms or molecules of gas in interstellar space, making up about 99% of the interstellar medium. Depending on density, the number of atoms range from 0.1 to 1 atoms per cubic centimetre of normal space, with up to 1000 per cubic centimetre in gas clouds. About 75% is hydrogen, the remainder being helium, with traces of other elements.
>