Also known as Abell 85 or LBN 576 and more casually as the popped balloon, garlic, or the medulla nebula, CTB1 is a relatively faint supernova remnant located in Cassiopeia that has the distinction of being the closest SN remnant to planet Earth. Although Abell was the one to discover the target in 1955, it is not a planetary nebula as first thought, so CTB1 is probably the best designation. Located approximately 10k ly away, it is approximately the same size as the full moon. In addition, the image contains a possible planetary nebula PN We 2-262, the loop-like structure seen in the lower right, as well as the open cluster NGC 7788 in the upper right. Shot in SHO with RGB stars, the OIII signal was exceptionally faint, and the Sii signal asymmetrically overlapped with the shell of CTB1 itself. Still, there was enough difference between Ha and Sii to tease out a little more structure. Also uploaded is the starless version to better illustrate the SHO details. The full star field version is also included, though I found the full field distracting, and therefore have selected the reduced star field as the final image using
@Bill Blanshan's excellent tools.
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