The Veil Nebula, also known as the Cygnus Loop or the Witch's Broom Nebula, is a large, relatively faint supernova remnant in the constellation Cygnus. The source supernova exploded some 5,000 to 8,000 years ago, and the remnants have since expanded to cover an area of 3 degrees. The distance to the nebula is not precisely known, with estimates ranging from 1,400 to 2,600 light-years. It was discovered on 1784 September 5 by William Herschel. He described the western end of the nebula as "Extended; passes thro' 52 Cygni... near 2 degree in length." and described the eastern end as "Branching nebulosity... The following part divides into several streams uniting again towards the south."
The Hubble Space Telescope captured images of the nebula. The analysis of the emissions from the nebula indicate the presence of oxygen, sulfur, and hydrogen.
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 only visible 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.
The nebula is notorious among astronomers for being difficult to see visually, even though it has a bright integrated magnitude of 7. However, a telescope using an OIII filter (a filter isolating the wavelength of light from doubly ionized oxygen), will allow an observer to see the nebula clearly, as almost all light from this nebula is emitted at this wavelength. Using an 8-inch (200 mm) telescope equipped with an OIII filter, one could easily see the delicate lacework apparent in photographs. With an OIII filter, almost any telescope could conceivably see this nebula, and some argue that it can be seen without any optical aid, excepting an OIII filter held up to the eye. This is also one of the largest, brightest features in the x-ray sky.
Citation Text: Wikipedia
Image Credit: T. Rector/University of Alaska Anchorage and WIYN/NOAO/AURA/NSF