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CTB is a supernova remnant (leftovers from an exploding star), similar to the famous Veil Nebula in Cygnus but much fainter. Its size in the sky is similar to the size of a full moon and it is approximately circular. Note, however, that its outer shell has ruptured between the 4 and 5 o'clock position. Originally this was thought to be a planetary nebula (which is why it appears as Abell 85 in his catalogue of planetaries) but in 1971 it was determined that it is actually a supernova remnant.
CTB 1 is quite faint so a total of 30 hours of exposure was used to capture it (12 hours of H-alpha and 18 hours of O-III).