... Silhouetted by the glowing interstellar clouds and crowded star fields, the dark Northern Coal Sack is also visible, part of a series of obscuring dust clouds forming the Great Rift in the Milky Way . These Cygnus nebulosities are all located about 2,000 light-years away. ... NASA Web Site Statements, Warnings, and Disclaimers . ... Publications with keywords: Cygnus - emission nebula - dark nebula - H-alpha . Publications with words: Cygnus - emission nebula - dark nebula - H-alpha . ...