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 and Simeis 188) 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 CTB 1 and Simeis 147 are especially dim and represent some of the faintest objects in the sky.

Note: The extended galactic supernova remnant CTB 1 in Cassiopeia is one of the closest SNR's known lying at a distance of about 9,800 light-years away. Measuring approximately 35.2 arc-minutes in diameter and physically spanning 98 light-years across, this circular formation rich with filamentary structure lies immediately east of Caph (β-Cas, mag 2.26) and is characterized with dominant optical, x-ray and radio sources. CTB 1 was originally thought to be a large planetary nebula and was included by Abell in his catalog of planetary nebula (Abell 85) but it was suggested by van den Bergh in 1960 and comfirmed by Willis & Dickel in 1971 to be, in fact, not a planetary nebula but rather a galactic SNR.

The northeast portion of the shell is discontinuous and studies have confirmed this shell rupture to be genuine and not an optical illusion and to extend up to 30' to the east and past the main shell. Also of interest is the stronger O-III emission on the western section of the shell and which coincides with scientific findings and is believed to represent "large-scale, incomplete shock cooling". Similarly, the greater contrast of the southern half of CTB 1 is consistent with scientific findings and which has been linked to the various dust clouds in the immediate area and also visible in the image below.