Abell 39 is a planetary nebula with low surface brightness in the constellation Hercules. It shines predominantly in the blue light of the double ionized atomic oxygen [OIII].
It is assumed that the nebula is about 6800 light years away from Earth. It has an almost spherical geometry. The central star of the nebula is about 2″ (about 0.1 light years) west of the center. This does not seem to be due to an interaction with interstellar matter, but to a slight asymmetry in the distribution of matter ejected by the central star [Wikipedia].
Picture taken from the city of Wissen with an 8-inch RC telescope at f=1080mm focal length. Exposure time was 11 hours in four nights at the end of June 2019: [OIII ]: 26 x 15min; H-alpha:13 x 15min; R, G, B (for the star colors): 5 x 5min each.
Picture: Peter Stinner, member of the STScI. Text: Wikipedia
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