IC 5146 (also Caldwell 19 , Sh 2-125 , Barnard 168 , and the Cocoon Nebula ) is a reflection / emission nebula and Caldwell object in the constellation Cygnus . The NGC description refers to IC 5146 as a cluster of 9.5 mag stars involved in a bright and dark nebula. The cluster is also known as Collinder 470. It shines at magnitude +10.0/+9.3/+7.2. Its celestial coordinates are RA 21 53.5 , dec +47° 16′. It is located near the naked-eye star Pi Cygni , the open cluster NGC 7209 in Lacerta , and the bright open cluster M39 . The cluster is about 4,000 ly away, and the central star that lights it formed about 100,000 years ago; the nebula is about 12 arcmins across, which is equivalent to a span of 15 light years.
6-670: When viewing IC 5146, dark nebula Barnard 168 (B168) is an inseparable part of the experience, forming a dark lane that surrounds the cluster and projects westward forming the appearance of a trail behind the Cocoon. IC 5146 is a stellar nursery where star-formation is ongoing. Observations by both the Spitzer Space Telescope and the Chandra X-ray Observatory have collectively identified hundreds of young stellar objects . Young stars are seen in both
12-428: A molecular ion N 2 H ( diazenylium ), all of which are relatively transparent. These clouds are the spawning grounds of stars and planets, and understanding their development is essential to understanding star formation . The form of such dark clouds is very irregular: they have no clearly defined outer boundaries and sometimes take on convoluted serpentine shapes. The closest and largest dark nebulae are visible to
18-534: Is a type of interstellar cloud , particularly molecular clouds , that is so dense that it obscures the visible wavelengths of light from objects behind it, such as background stars and emission or reflection nebulae. The extinction of the light is caused by interstellar dust grains in the coldest, densest parts of molecular clouds. Clusters and large complexes of dark nebulae are associated with Giant Molecular Clouds. Isolated small dark nebulae are called Bok globules . Like other interstellar dust or material,
24-502: The emission nebula, where gas has been ionized by massive young stars, and in the infrared-dark molecular cloud that forms the "tail". One of the most massive stars in the region is BD +46 3474, a star of class B1 that is an estimated 14±4 times the mass of the sun . Another interesting star in the nebula is BD +46 3471, which is an example of a HAeBe star , an intermediate mass star with strong emission lines in its spectrum. Dark nebula A dark nebula or absorption nebula
30-638: The naked eye, since they are the least obscured by stars in between Earth and the nebula, and because they have the largest angular size , appearing as dark patches against the brighter background of the Milky Way like the Coalsack Nebula and the Great Rift . These naked-eye objects are sometimes known as dark cloud constellations and take on a variety of names. In the inner molecular regions of dark nebulae, important events take place, such as
36-501: The things it obscures are visible only using radio waves in radio astronomy or infrared in infrared astronomy . Dark clouds appear so because of sub-micrometre-sized dust particles, coated with frozen carbon monoxide and nitrogen, which effectively block the passage of light at visible wavelengths. Also present are molecular hydrogen, atomic helium, C O (CO with oxygen as the O isotope ), CS, NH 3 ( ammonia ), H 2 CO ( formaldehyde ), c-C 3 H 2 ( cyclopropenylidene ) and
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