Physical Information: Shown to consist of stars moving together in the 1800's, and currently thought to have a common origin with the open cluster known as Praesepe, around 625 million years ago. (Additional physical information and other images to be posted once all Caldwell objects have been added to this Catalog.

Historical References: Among the Australian aborigines, who like many primitive cultures used dark regions in the Milky Way as constellations, it was known as the head of the "emu in the sky". Vespucci referred to it as "the dark Canopus". It later became known as "Magellan's Spot", or the "Black Magellanic Cloud", as opposed to the bright Large and Small Magellanic Clouds (which are of course galaxies, and not part of the Milky Way). The term "coalsack" was long used for any dark region in the Milky Way, and what we now call the Coalsack Nebula only became the Coalsack Nebula in 1899, when Richard Hinckley Allen's Star-Names and Their Meaning (later republished as Star-Names -- Their lore and meaning) assigned "The Northern Coalsack Nebula" to an absorption feature in the Northern sky.
Physical Information: The nebula is a cloud of gas and dust less than 600 light-years from us, and although only about 30 to 35 light-years in size, its close proximity allows it to obscure a region about 7 by 5 degrees across, covering not only part of Crus, but also parts of Centaurus and Musca. It is slightly patchy, and although covering almost everything lying beyond it, there are places where more distant objects can be seen, and of course anything closer than the absorption nebula is also visible. Still, it is a very obvious and striking blot on the starry background of the Milky Way.