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
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 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.
