Total exposure time 58h

Two ways to end a life of the star in a same seven degrees field of view!

Just next to Sh2-221 locates a closest known planetary nebula, Sh2-216. This is also a very rarely images target, due to its low surface brightness and large angular dimension. This mosaic image covers over seven degrees of sky vertically. (The Moon has an apparent dimension of 0.5 degrees.) Mosaic is made out of my new data of Sh2-221 and an older material of Sh2-216. Some exposures was taken to match the background.

Image shows two different ways to end a life of the star. At left, as a Supernova and at right as a Planetary Nebula. (Massive stars will go to a Supernova, after burning out all of the Hydrogen. There will be a Neutron star or a Black Hole left behind. Lighter stars, as our Sun, will left a Planetary Nebula behind, after ran out of Hydrogen. There is a core of the star at the center of the nebula, it's called a White Dwarf and it will cool down gradually. )