| Dark nebula | |
|---|---|
 The Coalsack Nebula, taken by the Wide Field Imager on theMPG/ESO 2.2-metre telescope[1] | |
| Observation data: J2000.0epoch | |
| Right ascension | 12h 50m |
| Declination | −62° 30′ |
| Distance | 180[2] pc |
| Apparent magnitude (V) | – |
| Apparent dimensions (V) | 7° × 5° |
| Constellation | Crux |
| Physical characteristics | |
| Radius | 30–35 ly |
| Absolute magnitude (V) | – |
| Notable features | – |
| Designations | Caldwell 99 |
| See also:Lists of nebulae | |
TheCoalsack Nebula (Southern Coalsack, or simplytheCoalsack)[3] is adark nebula, which is visible to thenaked eye as a dark patch obscuring part of theMilky Way east ofAcrux (Alpha Crucis) in the constellation ofCrux.[2]
Historically any otherdark cloud in thenight sky was called coalsack. The Coalsack Nebula was juxtaposed in 1899 byRichard Hinckley Allen through naming theNorthern Coalsack Nebula.[4]
The Coalsack Nebula covers nearly 7° by 5° and extends into the neighboring constellationsCentaurus andMusca.[5] The first observation was reported byVicente Yáñez Pinzón in 1499.[6] It was named "il Canopo fosco" (the darkCanopus) byAmerigo Vespucci and was also called "Macula Magellani" (Magellan's Spot) or "Black Magellanic Cloud" in opposition to theMagellanic Clouds.[6]
InAustralian Aboriginal astronomy, the Coalsack forms the head of theemu in the sky in severalAboriginal cultures. Amongst theWardaman people, it is said to be the head and shoulders of alaw-man watching the people to ensure they do not break traditional law. According to a legend reported by W. E. Harney, this being is calledUtdjungon and only adherence to the tribal law by surviving tribe members could prevent him from destroying the world with a fiery star.[7] There is also a reference by Gaiarbau (1880) regarding the coalsacks replicatingbora 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 ceremonial ring.
InInca astronomy this nebula was calledYutu, after a partridge-like South American bird,[8] orTinamou.[9]
The Coalsack Nebula appeared inKenji Miyazawa's storyNight on the Galactic Railroad, where the protagonist, Giovanni, experiences his friend, Campanella, departing to his personal afterlife referred to as "True Heaven" where he sees his dead mother waiting for him. Giovanni is unable to see True Heaven, and is represented, instead, as the empty, black Coalsack to Giovanni.
The Coalsack Nebula and the galactic area surrounding it played a large role inJerry Pournelle'sCoDominium Universe, particularlyThe Mote in God's Eye and the sequelThe Gripping Hand, both co-authored withLarry Niven. In these novels, a human-colonized system, New Caledonia, is on the opposite side of the Coalsack from Earth. Set against the Coalsack is a red supergiant, and between the supergiant and New Caledonia is a yellow F6 star, known as "The Mote in God's Eye".
