The Coalsack Nebula (Southern Coalsack, or simply the Coalsack) is the most prominent dark nebula in the skies, being easily visible to the naked eye as a dark patch obscuring a brief section of Milky Way stars as they cross their southernmost region of the sky, east of Acrux (Alpha Crucis) which is the bright, southern pointer star of the southern cross. It dominates and overspills the southeast corner of what is considered the extent of the constellation Crux at a little less than twice the distance of Acrux, 180 parsecs (590 ly) away from Earth.
The Coalsack Nebula covers nearly 7° by 5° and overlaps somewhat with the neighbor constellations Centaurus and Musca. The first observation was reported by Vicente Yáñez Pinzón in 1499. It was named "il Canopo fosco" (the dark Canopus) by Amerigo Vespucci and was also called "Macula Magellani" (Magellan's Spot) or "Black Magellanic Cloud" in opposition to the Magellanic Clouds.
The Coalsack is omitted in most of today's standard catalogs on the Milky Way such as the New General Catalogue and its only mainstream identification number is in the somewhat specialist Caldwell catalogue, in which it is C99.
A depiction of the emu in the sky
, which is an Australian Aboriginal constellation consisting of dark clouds rather than of stars. The European constellation on the right is Crux
, or the Southern Cross, and on the left is Scorpius
. The head of the emu is the Coalsack.
The Coalsack in Australian Aboriginal astronomy forms the head of the emu in the sky in several Aboriginal cultures. Amongst the Wardaman people, it is said to be the head and shoulders of a law-man watching the people to ensure they do not break traditional law. According to a legend reported by W. E. Harney, this being is called Utdjungon and only adherence to the tribal law by surviving tribe members could prevent him from destroying the world with a fiery star. There is also a reference by Gaiarbau (1880) regarding the coalsacks replicating bora rings on Earth. These astronomical sites allowed the spirits to continue ceremony similar to their human counterparts on Earth. As bora grounds are generally located on the compass points north/south, the southern coal sack indicates the initiation/ceremonial ring.
In Inca astronomy this nebula was called Yutu, meaning a partridge-like southern bird or Tinamou.
The dark Coalsack Nebula can be seen as an obscuring smudge across the Milky Way
The Coalsack is mentioned in the Star Trek: The Original Series episodes "The Immunity Syndrome" and "Let That Be Your Last Battlefield", as well as 2001: A Space Odyssey by Arthur C. Clarke.
In the Solar Queen series by Andre Norton, several characters swear "...by the Coalsack's Ripcord!"
The Coalsack figures prominently in the Larry Niven and Jerry Pournelle's science fiction novel The Mote in God's Eye and its sequels, The Gripping Hand and Outies.
Also, Henry De Vere Stacpoole described the Coalsack in his novel The Blue Lagoon (1908), as Lestrange observes it from the deck of the Northumberland, "In the Milky Way, near the Southern Cross, occurs a terrible circular abyss, the Coal Sack. So sharply defined is it, so suggestive of a void and bottomless cavern, that the contemplation of it afflicts the imaginative mind with vertigo. To the naked eye it is as black and dismal as death, but the smallest telescope reveals it beautiful and populous with stars. Lestrange's eyes travelled from this mystery to the burning cross, and …"
The Coalsack is mentioned in the Futurama episode "Hell Is Other Robots".
In the film Night on the Galactic Railroad and the original children's story of which it is based from, the journey for the character Campanella ends with him going to the Coalsack.
In the film The Chronicles of Riddick, the character Imam convinces Riddick to help his people against the Necromongers and says, "The Coalsack planets are gone."
In Brian J. Clarke's novella The Expediter, a world of mysterious towers—and the aliens studying them—are found "behind the Coalsack".
In the game Elite Dangerous players can visit the Coalsack Nebula, designated in the game with the system prefix "MUSCA DARK REGION". 
In The Star Kings by Edmond Hamilton Coalsack is the home of The League of Dark Worlds, most powerful military dictatorship in the Galaxy.
The Coalsack Nebula can be seen as the large dark region near the top of the photo
- ^ "A Cosmic Sackful of Black Coal". Retrieved 15 October 2015.
- ^ a b Franco, G.P.A. (2000). "Interstellar Na I D lines towards the Southern Coalsack". Monthly Notices of the Royal Astronomical Society. 315 (3): 611–621. Bibcode:2000MNRAS.315..611F. doi:10.1046/j.1365-8711.2000.03434.x.
- ^ "Coalsack Nebula". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-09-30.
- ^ Darling, David J. (2004). The universal book of astronomy: from the Andromeda Galaxy to the zone of avoidance. Hoboken, New Jersey: Wiley. p. 351. ISBN 0471265691.
- ^ a b "The Coalsack and the Southern Cross". ESO. 3 December 2009. Retrieved 1 October 2018.
- ^ Songs of the Songmen, 28–30.
- ^ James B. Kaler (2002). The Hundred Greatest Stars. New York: Springer Science & Business Media. p. 5. ISBN 978-0-387-95436-3.
- ^ A. F. Aveni, ed. (2010). Archaeoastronomy in the New World : American primitive astronomy : proceedings of an international conference held at Oxford University, September, 1981. Cambridge: Cambridge University Press. ISBN 978-0521125475.
- ^ "An Emu in the Sky over Paranal". www.eso.org. European Southern Observatory. Retrieved 1 October 2014.
- ^ https://www.gutenberg.org/files/16921/16921-h/16921-h.htm
- ^ Pournelle, Jennifer R. (30 March 2011). Outies. ISBN 978-0615434148.
- ^ H. De Vere Stacpoole: ‘The Blue Lagoon’, London: Adelphi Terrace, 1908, T. Fisher Unwin Ltd., quote taken from 28th Impression (1923), p. 12, from pdf p. 28 at https://archive.org/details/bluelagoonromanc00stacrich.
- ^ http://theinfosphere.org/Hell_Is_Other_Robots
- ^ http://www.script-o-rama.com/movie_scripts/c/chronicles-of-riddick-script-transcript.html
- ^ "The Coalsack & Chameleon Nebulae". Retrieved 2021-01-29.
- ^ Hamilton, Edmond (1949). The Star King. ISBN 9780575133167.