|Right ascension||12h 50m|
|Type of object||Dark nebula|
|Distance from Earth||600 ly|
The Coalsack nebula (C99) is a dark nebula found in the constellation of Crux, the Southern Cross. It also partially overlaps into the constellations of Musca and Centaurus. Along with the Horsehead nebula, it is one of the best known dark nebulae and visible in the Southern hemisphere. The nebula is not listed in the New General Catalogue. Then nebula is sometimes nicknamed the Black Magellanic Cloud, a joke comparing its dark appearance to the brightness of the Magellanic Clouds.
The nebula is sufficiently large that it is easily seen with the naked eye. A such, it has been known such ancient times. It was first recorded by a European in 1499, by the Spanish navigator Vicente Yáñez Pinzón on his journey to South America. The first proper description of the object was provided by Peter Martyr d’Anghiera, at some point between 1511 and 1521. Much later in 1970, the Finish astronomer Kalevi Mattila demonstrated that the nebula is not completely black, but instead has 10% the brightness of the surrounding Milky Way. This light derives from the reflection of the light of stars obscured by the nebula. Background stars are visible in observations with the latest telescopes.
As it has been known since prehistoric times, there are many myths and legends surrounding the Coalsack nebula. The Incas believe the Coalsack nebula is where their god, Ataguchu, kicked the Milky Way. A piece flew off and the nebula is what remains. The Aboriginal Australians believe that the nebula forms the head of an emu, whose body stretches down across Scorpius.
Properties and Structure
The Coalsack nebula is formed of thick clouds of dust and gas, roughly 30-35 light years across. Large numbers of these dust particles have been found to possess coatings of water ice, nitrogen, carbon monoxide as well as simple organic molecules. In fact studies of light extinction of stars behind the nebula have shown the nebula is made from two large overlapping dust clouds, at distances of 610 and 790 light years. These clouds have masses on the order of thousands of times that of the Sun.
Although the nebula appears dark, 10% of the background light does make it through the nebula. This light is reddened due to blue light being scatted off the dust, in a similar manner to how the Sun appears redder at sunset.