The Medusa Nebula is a large planetary nebula in the constellation of Gemini on the Canis Minor border. It also known as Abell 21 and Sharpless 274. It was originally discovered in 1955 by UCLA astronomer George O. Abell, who classified it as an old planetary nebula. The braided serpentine filaments of glowing gas suggests the serpent hair of Medusa found in ancient Greek mythology.
Until the early 1970s, the Medusa was thought to be a supernova remnant. With the computation of expansion velocities and the thermal character of the radio emission, Soviet astronomers in 1971 concluded that it was most likely a planetary nebula.
This image is a combination of long exposed narrowband-data (Ha/OIII) with a classical LRGB. North is about upper right of the image. The galaxy group left of the nebula is ranging between mag 18.2 (PGC 1422135) and mag 18.8 (PGC 1421175).
Telescope: RCOS 14.5" f/8
Mount: ASA DDM85
Detector: Apogee U16M
Filters: Astrodon Gen 2, 3nm/5nm Narrowband
Exposures: HaOIIILRGB 960:480:400:220:220:220 min
Observatory: ROSA, France