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A '''dark nebula''', also known as an absorption nebula, is a type of [[nebula]] formed from [[gas]] and [[dust]] and visible because it blocks out and absorbs light from [[star]]s or bright nebulae behind.<ref>[http://www.messier.seds.org/dark.html Dark nebulae] from messier.seds.org</ref> Dark nebulae may also contain stars, but these are obscured by the nebula. Well known examples of dark nebulae include the [[Horsehead nebula]] and the [[Coalsack nebula]]

A '''dark nebula''', also known as an absorption nebula, is a type of [[nebula]] formed from [[gas]] and [[dust]] and visible because it blocks out and absorbs light from [[star]]s or bright nebulae behind.<ref>[http://www.messier.seds.org/dark.html Dark nebulae] from messier.seds.org</ref> Dark nebulae may also contain stars, but these are obscured by the nebula. This dust also prevents light from stars outside the nebula from reaching its interior, making the centres of dark nebulae some of the coldest places in the [[universe]].<ref>[https://apod.nasa.gov/apod/dark_nebulae.html Astronomy Picture of the Day Index - Nebulae: Dark Nebulae] from apod.nasa.gov</ref> Well known examples of dark nebulae include the [[Horsehead nebula]] and the [[Coalsack nebula]]

==Properties==

==Properties==