Abell 39 is a low surface brightness planetary nebula in the constellation of Hercules at a distance of about 6'800 light-years and an apparent diameter of 3'. It's shell is nearly uniform spherical. However the western limb of the nebula is 50% more luminous than the eastern limb. It's central 15.5mag star is slightly east off-center by about 2". There is faint halo that extents beyond the bright rim.
This image was taken mostly through OIII filter (5nm) to bring out as much contrast as possible. It reveals structures within the planetary and the variations of the brightness of the rim. The faint halo is best visible at the upper part of the sphere. North is down on this image.
Telescope: RCOS 14.5" f/8
Mount: ASA DDM85
Filters: Astrodon Gen 2 5nm Narrowband
Exposures: Ha 200min OIII 800 min (40 min subs)