Astr111 Photography Projects, Fall 2004

Cocoon Nebula, John Van Hofwegen

The Cocoon nebula, which is catalogued as IC 5146, is about 4000 light years away. It is located in the constellation of Cygnus at Right Ascension 21h 53m 30s and Declination +47 15' 41”. It consists of an open star cluster at the tail end of the dark nebula, B 168, which is a large cloud of molecular dust and gas. Open star clusters are groups of stars that are held together by a gravitational pull. They share the same relative age, distance, and chemical composition; however, they differ in mass. The Cocoon nebula is very faint, impossible to see without a telescope. It is also relatively small, containing only about 20 stars.

This particular nebula is both a reflection and an emission nebula. A reflection nebula contains dust particles which reflect incident light. Emission nebulae give off light as result of heat. This heat comes from the massive bright stars within the nebula itself. The reddish hue tells us that the nebula contains a lot of hydrogen. This is because hydrogen, when excited by heat, gives off light, red being the strongest emission.