Molecular Cloud

Molecular cloud, also called dark nebula is an interstellar clump or cloud that is opaque to its internal dust grains. The form of such dark clouds is irregular: they don’t have a clearly defined external boundaries and sometimes undertake convoluted serpentine shapes as a consequence of turbulence. The largest molecular clouds are visible towards naked eye, appearing as dark patches up against the brighter background in the Milky Way Galaxy. An example is the Coalsack in this southern sky.