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.[4]
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 8-inch
(200 mm) telescope with an
[O III]
filter to find this object although probably possible to image with
smaller apertures (*)
(*) Source Wilkipedia