Abell 31 or SH2-290 is an ancient planetary nebula in the constellation of Cancer. It is estimated to be about 2,000 light years away.
Although it is one of the largest planetary nebulae in the sky, extending 17 arc-min, it is very dim. The surface brightness is about 26,9 Mag/arc-sec².
The southern part of the nebula is showing a distinct rounded shock front, the northern part is mixing with the surrounding interstellar matter.
This dissipation is showing the high age of the nebula.
Ha-OIII-LRGB (400-400-440-140-140-140 min), total 27,6 h, Seeing 0.8-1.2 arcsec, North is up;
80cm f/7 Astrooptik Keller corrected cassegrain, FLI Proline 16803, Astrodon Gen2 filters, Prompt 7 CTIO Chile
Processing: Johannes Schedler
Find the combined Ha-OIII-LRGB image of the full field below in 25/60 % size.