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|Observation data: J2000.0 epoch|
|Right ascension||12h 50m|
|Apparent magnitude (V)||–|
|Apparent dimensions (V)||7° × 5°|
|Radius||30–35 ly ly|
|Absolute magnitude (V)||–|
The Coalsack Dark Nebula (or simply the Coalsack) is the most prominent dark nebula in the skies, easily visible to the naked eye as a dark patch silhouetted against the southern Milky Way. It is located at a distance of approximately 600 light years away from Earth, in the constellation Crux.
The Coalsack Dark Nebula covers nearly 7° by 5° and overlaps somewhat into 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.
In 1970, Kalevi Mattila proved that the Coalsack is not totally black. It has a very dim glow (10% of the brightness of the surrounding Milky Way), which comes from the reflection of the stars it obscures.
The Coalsack is important in Australian Aboriginal astronomy and 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.
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 …"
In the film Night on the Galactic Railroad, the character Campanella ends going to the Coalsack.
In Brian J. Clarke's novella The Expediter, a world of mysterious towers – and the aliens studying them – are found "behind the Coalsack".
- "A Cosmic Sackful of Black Coal". Retrieved 15 October 2015.
- 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.
- Songs of the Songmen, 28–30.
- p. 5, The Hundred Greatest Stars, James B. Kaler, New York, Copernicus Books, 2002.
- 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 0521125472.
- "An Emu in the Sky over Paranal". www.eso.org. European Southern Observatory. Retrieved 1 October 2014.
- 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.
- Starry Night Photography: Coalsack Dark Nebula
- Starry Night Photography: The Emu
- SIMBAD: Coal Sack Nebula