Abell 39 is an unusually spherical example of a "planetary nebula,"
which has nothing to do with planets (except that through a telescope
these objects tend to look like the disks of planets), but is in fact
the expelled outer layers of a star which has come to the end of
its fuel. This particular example appears to be a nearly perfect sphere.
Though the material which makes up this sphere of stellar gasses is
estimated to be equal to more than half the mass of our sun, its very
thin concentration is demonstrated by the fact that at least one
galaxy, far in the distance, is visible right through the nebula.
In fact, there are hundreds of very small, very dim galaxies visible
throughout this image.

Abell 39 has been expanding since the star at its center released this
bubble of gas 22,000 years ago, and is now about 5 light years in diameter.
It is 7000 light years from earth, in the constellation Hercules.

Image data:
Telescope: Hyperion 12.5"
Camera: SBIG STL-11000
Exposure: 10 1/2 hours (Luminance 360 minutes; RGB 270 minutes