Abell 21 is a large, faint, planetary nebula located in Gemini near the border of Canis Minor. It is known as the Medusa Nebula.

The hot magnitude 15.9 central star that powers the ionization of the nebula can be seen in the center of the nebula.

The Medusa nebula has an apparent brightness of magnitude 14.1 but appears fainter because its light is spread out over a large area. It is located 1,500 light-years away with an apparent size of 13 x 10 arcminutes, which corresponds to a real size of 4 light-years in space.

The Medusa was discovered by George O. Abell in 1955.

North is to the top in the above image.

Abell 21 Catalogs: Abell 21, PK 205+14.1, Sh2-274 Common Name: Medusa Nebula Object Type: Planetary Nebula Magnitude: 14.1 Size: 13' x 10' Constellation: Gemini Image Field Centered At: RA: 07h 29m 05s Dec: +13° 14' 19"