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The Medusa Nebula, also known as Abell 21, 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. The Medusa Nebula is estimated to be over 4 light-years across.
Wide angle view of NGC 2264 - Christmas Tree open star cluster, including the Cone Nebula (atop the tree), variable star S Mon (near blue reflection nebula), and the Fox Fur Nebula (inside the blue-tinted doughnut shaped reflection nebula. All about 2,500 light years distant in the constellation Monoceros (the unicorn). This picture spans an area of the sky about 1.5 full moons covering 40 light-years at the distance of NGC 2264.
Massive star IRS 4 is beginning to spread its wings. Born about 100,000 years ago, material streaming out from this newborn star has formed the nebula dubbed Sharpless 2-106 Nebula (S106), pictured above. It lies about 2000 light-years away toward the constellation of the Swan (Cygnus).
The Ring Nebula is a planetary nebula in the constellation of Lyra about 4000 light-years away.