Object Analysis

The Medusa Nebula (Abell 21) is a large planetary nebula in the constellation Gemini. It was discovered in 1955 by George O. Abell. It gets its name from its braided filaments of glowing gas, which resemble the snake-hair of the mythological Gorgon, Medusa.

Until the 1970s, the Medusa was thought to be a supernova remnant because of its large size and irregular shape. However, spectral analysis eventually confirmed it is a very old planetary nebula. The central star is no longer at the geometric center because it is moving through the interstellar medium, leaving the "hair" of the nebula behind it.

Located about 1,500 light-years away, the Medusa is very faint and requires a large telescope and specialized filters to be seen. The red glow is ionized hydrogen, while the greenish-blue highlights come from oxygen. It is a haunting example of a stellar remnant in its final stages of dissipation.