暗星云是星际云（ interstellar cloud）的一种，他的密度足以屏蔽来自背景的发射星云或反射星云的光（像是马头星云），或是屏蔽背景的恒星（像是煤炭袋）。

天文学上的消光通常来自大的分子云内温度最低、密度最高部份的星际尘埃颗粒。大而复杂的暗星云聚合体经常与巨大的分子云联结在一起，小且孤独的暗星云被称为包克球。

这些暗星云的形成通常是无规则可循的：它们没有被明确定义的外型和边界，有时会形成复杂的蜒蜒形状。巨大的暗星云以肉眼就能看见，在明亮的银河中呈现出黑暗的补丁。

在暗星云的内部是发生重要事件场所，像是恒星形成和迈射。

A dark nebula or absorption nebula is a type of interstellar cloud that is so dense it obscures the light from objects behind it, such as background stars and emission or reflection nebulae. The extinction of the light is caused by interstellar dust grains located in the coldest, densest parts of larger molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules. Like other interstellar dust or material, things it obscures are only visible using radio waves in radio astronomy or infrared in infrared astronomy.