Ancient Photons Observatory: Cygnus Loop

The Cygnus Loop is a large supernova remnant in the constellation Cygnus, an emission nebula measuring nearly 3° across. Some arcs of the loop, known collectively as the Veil Nebula or Cirrus Nebula, emit in the visible electromagnetic range. Radio, infrared, and X-ray images reveal the complete loop.

The nebula was discovered on 5 September 1784 by William Herschel. He described the western end of the nebula as "Extended; passes through 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.

A more recent investigation of the Cygnus Loop's distance using Gaia parallax measurements of several stars seen toward the Cygnus Loop has led to a more accurate distance estimate. One of these stars, a 9.6 magnitude B8 star (BD+31 4224) located near the remnant's northwestern rim shows evidence of interactions of its stellar wind with the Cygnus Loop's shock wave, thereby indicating it is located actually inside the remnant.