Supernova remnants represent the residual effects of massive stars which have reached the end of their life-cycle, including a massive stellar explosion as a grand finale, and which leave behind them spectacular gas clouds and stellar remnants (neutrinos) which cover multiple full moons in width across the sky. Regrettably, for residents of the northern hemisphere, only four supernova remnants (SNR) are visible and, more specifically, the Crab Nebula (M1) in Taurus, the massive Veil complex (NGC 6960, 6974, 6979, 6992, 6995) in Cygnus, the Jellyfish Nebula (IC 433) in Gemini and Simeis 147 (aka Shajn 147, Sh 2-240) also in Taurus. The most recognized supernova remnant is perhaps the Crab nebula in Taurus which is believed to have exploded in 1054 AD as documented by Chinese astronomers of the time whereas Simeis 147 is especially dim and represents one of the faintest objects in the sky.

Note: For an excellent article on observing supernova remnants, see Astronomy Magazine (Sept/2006: 64-67).