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
AI 生成的摘要
美杜莎星云（又称阿贝尔21）是一个距离地球约1500光年的老行星状星云，位于双子座。它的名字源于其发光气体的编织和蛇形丝状结构，象征着戏剧性的转变。这个星云代表了低质量恒星（如太阳）演化的最终阶段，从红巨星转变为热白矮星，并在此过程中抛弃外层。热星发出的紫外线辐射使星云发光。美杜莎星云的直径估计超过4光年。