The Cygnus Loop . ... Credit Copyright: J. Hester ( ASU ), NASA Explanation: The shockwave from a 20,000 year-old supernova in the constellation of Cygnus supernova explosion is still expanding into interstellar space. The collision of this fast moving wall of gas with a stationary cloud has heated it causing it to glow in visible as well as high energy radiation , producing the nebula known as the Cygnus Loop (NGC 6960/95). The nebula is located about 2500 light-years away. ...