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 [
http://www.seds.org…] some 1,500 light-years away in the constellation Gemini [ http://en.wikipedia. org/wiki/Gemini_(con stellation) ]. Like its mythological [
http://en.wikipedia…] namesake, the nebula is associated with a dramatic transformation. The planetary nebula [
http://www.noao.edu…] phase represents a final stage in the evolution [
http://casswww.ucsd…] of low mass stars like the sun [
http://www.astro.wa…], as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation [
http://hyperphysics…] from the hot star powers the nebular glow. The Medusa's transforming hot central star is visible in the detailed color image [
http://dg-imaging.a…display.cfm?imgID=10 6 ] as the small blue star within the upper half of the overall bright crescent shape [
http://www.noao.edu…]. Fainter filaments clearly extend above and to the left of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.
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 [
http://www.seds.org…] some 1,500 light-years away in the constellation Gemini [ http://en.wikipedia. org/wiki/Gemini_(con stellation) ]. Like its mythological [
http://en.wikipedia…] namesake, the nebula is associated with a dramatic transformation. The planetary nebula [
http://www.noao.edu…] phase represents a final stage in the evolution [
http://casswww.ucsd…] of low mass stars like the sun [
http://www.astro.wa…], as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation [
http://hyperphysics…] from the hot star powers the nebular glow. The Medusa's transforming hot central star is visible in the detailed color image [
http://dg-imaging.a…display.cfm?imgID=10 6 ] as the small blue star within the upper half of the overall bright crescent shape [
http://www.noao.edu…]. Fainter filaments clearly extend above and to the left of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across.
Explanation
