IC 5146, 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 shines at magnitude +10.0/+9.3/+7.2. It is located near the naked-eye star Pi Cygni.
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.
IC 5146 is a stellar nursery where star-formation is ongoing. Young stars are seen in both the emission nebula, where gas has been ionized by massive young stars, and in the infrared-dark molecular cloud that forms the “tail”. 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.