Supernova Remnant Sh2-240 in the constellation Taurus. Also called Semeis 147. There is a repidly pulsating neutron star inside of it that is thought to be the remnant of the star that caused the catastrophe.

One of the dimmest objects in the night sky, this supernova remnant requires long exposures to capture it's wispy filaments. It is over 3 degrees wide, or about the width of 6 full moons. I used a 300mm camera lens to cover that wide field of view. With my best background levels getting within 10 ADU of the dimmest signal, imaging this object led to an education in the minutiae that degrade images. Nearby lights and lower altitude subframes led to slightly higher background levels and tossed frames, imperfect focus and wind gusts caused reduced S/N and FWHM and some more tossed frames. I used the best 9 out of 18 subframes.