The Medusa Nebula is a planetary nebula in the constellation of Gemini. It is also known as Abell 21 and Sharpless 2-274. It was originally discovered in 1955 by University of California, Los Angeles astronomer George O. Abell, who classified it as an old planetary nebula. 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 large, its surface brightness is very low, with surface magnitudes of between +15.99 and +25 reported. The central star of the planetary nebula is a PG 1159 star.
See also Abell Catalog of Planetary Nebulae List of planetary nebulae Geminga, Gemini gamma-ray source Gemini in Chinese astronomy IC 444, reflection nebula Messier 35 open cluster Cancer Minor (constellation) - Obsolete constellation inside modern Gemini
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