Image Credit & Copyright: Ken Crawford (Rancho Del Sol Obs.)
Explanation: Braided, 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 nebulaphase 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 near the center of the overall bright crescent shape. In
this deep telescopic view, fainter filaments clearly extend below and to the left of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.
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