Explanation: Braided and serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away in the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. The Medusa's transforming star is the faint one near the center of the overall bright crescent shape. In this deep telescopic view, fainter filaments clearly extend below and to the left. The Medusa Nebula is estimated to be over 4 light-years across.
The Medusa Nebula
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メデューサ星雲（Abell 21）は、約1,500光年離れた双子座に位置する古い惑星状星雲です。光るガスの絡み合ったフィラメントが特徴で、神話のメデューサにちなんで名付けられました。この星雲は、太陽のような低質量星が赤色巨星から熱い白色矮星に変化する最終段階を示しています。中心にある淡い星からの紫外線が星雲の光を生み出しています。メデューサ星雲は約4光年の大きさと推定されています。