Abell 39 is an almost perfectly spherical planetary nebula in the constellation Hercules. Discovered in 1966 by George Abell, it is one of the largest known spheres in our Galaxy. Its shape has allowed astronomers to accurately estimate how much relative material in the nebula is absorbing and emitting light. Observations indicate that Abell 39 contains has only about half the abundance of oxygen found in the sun. The reason why the central star is slightly off center, by 0.1 light-year, is currently unknown.

visual magnitude	13.7 (integrated); 15.7 (central star)
angular diameter	3.9'
linear diameter	5 light-years
distance	~ 7,000 light-years
position	R.A. 16h 27m 32.6s; Dec. +27° 54' 29"
other designations	PNG 047.0+42.4, PK 047+42.1, ARO 180