Constellation: Cygnus
Distance: 4,700 light years
Magnitude: 10 
Visual Size: 20.0 x 10.0 arcminutes
Other Designations: Sharpless 105, Caldwell 27

The nebula was discovered on 5th September 1784 by William Herschel.  He described the western end of the nebula as “Extended; passes thro’ 52 Cygni… near 2 degrees in length”, and described the eastern end as “Branching nebulosity… The following part divides into several streams uniting again towards the south.”

When finely resolved, some parts of the image appear to be rope-like filaments. The standard explanation is that the shock waves are so thin, less than one part in 50,000 of the radius, that the shell is visible only when viewed exactly edge-on, giving the shell the appearance of a filament. Undulations in the surface of the shell lead to multiple filamentary images, which appear to be intertwined.

Even though the nebula has a relatively bright integrated magnitude of 7, it is spread over so large an area that the surface brightness is quite low, so the nebula is notorious among astronomers as being difficult to see. However, an observer can see the nebula clearly in a telescope using an OIII filter (a filter isolating the wavelength of light from doubly ionized oxygen), as almost all light from this nebula is emitted at this wavelength. An 8-inch (200 mm) telescope equipped with an OIII filter shows the delicate lacework apparent in photographs, and with an OIII filter almost any telescope could conceivably see this nebula. Some argue that it can be seen without any optical aid except an OIII filter held up to the eye.