Network nebula — Supernova Remnant in Cygnus

NGC 6995 is the brightest knot of the Eastern Veil Nebula, part of the vast Cygnus Loop supernova remnant in the constellation Cygnus. The full loop spans about 3 degrees and is the expanding shock shell of a supernova that exploded roughly 10,000 to 20,000 years ago, some 1,500 light-years from Earth. NGC 6995 specifically forms the southern end of the eastern arc and is often called the Network Nebula for its intricate filamentary structure. Adjacent NGC 6992 continues the arc to the north. Together they complement the western Witch's Broom (NGC 6960) to form the complete 'Veil' visible in wide-field images.

One of the most filter-dependent objects in the sky — without an OIII filter it is faint and diffuse; with one, it snaps into a breathtaking lace of filaments. An OIII filter is essentially mandatory; a UHC works reasonably well; no-filter views are a letdown. A 6-inch telescope at 50x with OIII already shows the structure clearly. An 8-10 inch scope with OIII is spectacular — the eastern arc looks like a river delta of braided streams of light. Use the lowest power that keeps the filter dark enough; a 2-inch OIII plus a wide-field eyepiece is ideal. Best observed July through November.

Discovered by William Herschel on September 7, 1784 using his 18.7-inch reflector, on the same night he found NGC 6992 and several other Veil components. Herschel cataloged each bright knot separately, not realizing they were parts of a single supernova remnant — that interpretation came only in the 20th century. The Cygnus Loop was identified as a supernova remnant in the 1950s based on its expansion velocity and filamentary morphology, and it has since become one of the most-photographed nebulae in the sky.