Abell 21, the Medusa Nebula in the constellation Gemini.

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This is the faint but large planetary nebula known as the Medusa Nebula, but officially Abell 21 or PK 205+ in Gemini. It was discovered in 1955 and was once classified as a supernova remnant. The very sparse open cluster NGC 2395 is at upper right from the nebula. The nebula is thought to be 4 light-years across and 1500 light-years away.

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Photo credit: © Alan Dyer/Stocktrek Images / Alamy / Afripics
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