Abell 39 (PN A66 39) is a low surface brightness[4] planetary nebula in the constellation of Hercules.

[2] This offset does not appear to be due to interaction with the interstellar medium, but instead, it is hypothesized that a small asymmetric mass ejection has accelerated the central star.

[4] The mass of the central star is estimated to be about 0.61 M☉ with the material in the planetary nebula comprising an additional 0.6 M☉.

There is a faint halo that extends about 18″ beyond the bright rim giving a complete diameter of around 190″ under the assumption that this emission is uniform around the planetary nebula.

[4][1] This planetary nebula has been expanding for an estimated 11,000 years, based on an assumed expansion velocity between 32 and 37 km/s and a 0.4 parsec radius.