Let's look at a planetary nebula nearly perfect spherical shape, whose name Abell 39 (Abell 39).
Today in our galaxy "Milky Way" is known more than 1500 planetary nebulae that are astronomical substance consisting of ionized gas shell and the central star - a white dwarf. Planetary nebulae are fast in astronomical terms the phenomenon, which lasts only a few tens of thousands of years. For comparison, the life of the parent star is a few billion years.
An interesting example is the object of the planetary nebulae Abell 39. This nebula is notable for its almost perfect spherical shape. This "perfect lady" is also known under the designations PN A66 39, PN ARO 180, PK 047 42 1, PN G047.0 +42.4, and Abell 39.
According to scientists sphere diameter of this planetary nebula is about 5 light years, and the thickness of the light shell about one-third of one light year.
Abell 39 is in the constellation of Hercules at a distance of 7000 light years from Earth.
Planetary Nebula Abell 39 was opened in 1966 by the American astronomer George Abell, after whom it was named. Abell is known for a catalog of planetary nebulae with low surface brightness, and a catalog of galaxy clusters 2712.
The central star is associated with the nebula, is offset from the center of the sphere to the angular distance of about 0.1 light years. This shift does not yet have a clear scientific explanation, but it is assumed that it is due to a small asymmetry in the explosion of mass stars.
The shell of the nebula is quite transparent in the optical region and through it there are located on stars and galaxies.