This object glows faintly, but a small scope will let you see it.
The Cocoon Nebula (IC 5146) is on the left of this image. If you use a wide-field eyepiece, also look for the dark nebula Bernard 168, stretching to the right.
Credit: Michael Stacker
- The Cocoon Nebula, an emission nebula spanning 12 arcminutes (1/5 degree) in the Cygnus constellation, is about 4,000 light-years away and has a diameter of 15 light-years.
- This object overlaps the eastern boundary of Barnard 168 (B168), a prominent dark nebula, and contains a 9th-magnitude star cluster cataloged as Collinder 470 at the center.
- Discovered by Thomas Henry Aspinall Compton Aspin in 1899, the nebula was first photographed in 1900 by Maximilian Franz Joseph Cornelius Wolf, who described its unique surroundings “devoid of faint, faint stars”.
- While its integrated brightness is comparable to that of a 7th-magnitude star, the Cocoon Nebula’s low surface brightness and Collinder 470’s tangled stars require at least an 8-inch telescope and a nebula filter for better visual perception.
Some deep sky objects stand on their own. Others pair up with notable companions. Sometimes, the surrounding star field helps elevate the status of an ordinary object. Such is the case with the Cocoon Nebula, a 12′-wide (1/5°) emission nebula in the constellation Cygnus the Swan.
The Cocoon Nebula overlaps the eastern edge of Barnard 168 (B168), one of the finest dark nebulae in the northern sky. From a dark place, sharp-eyed observers can see this faint lane without optical aid, but it is not easy to see. A better approach is to use a telescope with a larger binocular or eyepiece that provides a field of view greater than 1°.
The Cocoon Nebula was discovered by British astronomer Thomas Henry Aspinel Compton Aspin on August 13, 1899. German astronomer Maximilian Franz Joseph Cornelius Wolf was the first to photograph it in 1900. Their description states, “It is centrally placed in a very fine lacuna devoid of faint stars, which surrounds the bright cloud like a moat. “The most striking thing about this object is that the star-zero halo that surrounds the nebula forms the end of a long channel… more than two degrees in length.”
In addition to the nearby dark nebula, Cocoon also contains a cluster of 9th-magnitude stars, cataloged as Collinder 470. Cocoon is located approximately 4,000 light years away. And it is not small. Its diameter is 15 light years.
You can see the Cocoon Nebula through a 4-inch telescope on a moonlit night, but only as a spherical hazy form. To find it, point your scope about 12° east of Deneb, Cygnus’ brightest star.
The luminosity of the cocoon is equivalent to that of a 7th-magnitude star, but the brightness of the nebula’s surface is lower because it is so diffuse. To make matters worse, Collinder 470’s stars are entangled in the brightness. For best results, use at least an 8-inch telescope and an eyepiece equipped with a nebula filter. The filter will suppress the starlight while still allowing most of the emission nebula’s brightness into your eyes. May you be successful!
