Medusa Nebula

The Medusa Nebula is a large planetary nebula in the constellation of Gemini on the Canis Minor border. It is also known as Abell 21 and Sharpless 2-274. 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.

As the nebula is so big, its surface brightness is very low, with surface magnitudes of between +15.99 and +25 reported.  Because of this most websites recommend at least an  telescope with an [O III] filter to find this object although probably possible to image with smaller apertures.

See also
 Abell Catalog of Planetary Nebulae　　　　　　　　　　　
 Abell 12　　　　　　　　　　　　　　　　　　　
 Abell 13　　　　　　　　　　　　　　　　　　　
Abell 33　　　　　　　　　　　　　　　　　　　
 Abell 39
 Abell 70
 Abell 78

References

External links
The Sharpless Catalog: Sharpless 274
APOD picture: The Medusa Nebula
Images of the Universe: PK 205+14.1 The Medusa Nebula in Gemini

Category:Planetary nebulae
Category:Gemini (constellation)
Category:Sharpless objects
21
Category:Astronomical objects discovered in 1955