A large supernova remnant in the constellation Cygnus at a distance of 1400 l.y. The loop is 3° across and expanding at over 100 km/s. It is about 5000 years old. Radio, infrared, and X-ray maps show a complete loop structure. However, optical telescopes show only fragments of the loop, notably the Veil Nebula.
Subjects: Astronomy and Astrophysics.