After almost 16 years, the Wide Field Planetary Camera 2 onboard the Hubble Space Telescope is being decommissioned. This image is its commemorative "final pretty picture."
The photograph (see it bigger!) is of the planetary nebula Kohoutek 4-55, in the constellation Cygnus, some 4,600 light years away. Layers of gas ejected by a dying red giant are ionized by radiation from the star's core, which causes them to glow.