Explanation:
Ghostly in appearance,
Abell 39
is a remarkably simple, spherical nebula about
five light-years across.
Well within our own
Milky
Way galaxy, the cosmic
sphere
is roughly 7,000 light-years distant toward the constellation
Hercules.
Abell 39 is a planetary nebula, formed as a
once sun-like star's outer atmosphere was expelled
over a period of thousands of years.
Still visible, the nebula's central star
is evolving into a hot white dwarf.
Although faint, the nebula's simple geometry has
proven to be
a boon
to
astronomers
exploring the chemical abundances and
life cycles of stars.
In
this deep image
recorded under dark night skies,
very distant
background
galaxies can be found --
some visible right through the nebula itself.
