The Medusa nebula, known scientifically as Abell 21, is an old planetary nebula some 1,500 light-years away in the constellation Gemini. It is estimated to be over 4 light-years across. This image was taken on Oct 24th, 2008 at the Mayall telescope with the mosaic camera, with [OIII] (assigned a blue color) and H-alpha (orange) filters This image was released during the 100 Hours of Astronomy webcast, "Around the World in 80 Telescopes" held from April 3-4, 2009, during the International Year of Astronomy 2009. View the recorded event from KPNO. See also this image of NGC 6520 from CTIO, which was also released during the webcast.
T. A. Rector/University of Alaska Anchorage and H. Schweiker/NOIRLab/NSF/AURA and NOIRLab/NSF/AURA