Explanation:
Except for the rings
of Saturn,
the Ring
Nebula (M57) is probably the most famous celestial band.
Its classic appearance is understood to be due to perspective -
our view from planet Earth looks down the center of a roughly
barrel-shaped cloud of glowing gas.
But expansive looping structures are seen to extend
far beyond
the Ring Nebula's familiar central regions in
this
intriguing composite of ground based and
Hubble Space Telescope images with narrowband
image data from Subaru.
Of course, in this well-studied example of a
planetary
nebula, the glowing material
does not come from planets.
Instead, the gaseous shroud represents outer layers expelled
from the dying,
once
sun-like star at the nebula's center.
Intense ultraviolet light from the hot central star
ionizes atoms in the gas.
Ionized oxygen atoms produce the characteristic greenish glow and
ionized hydrogen the prominent red emission.
The central ring of the Ring Nebula is about one light-year
across and 2,000 light-years away.
To accompany
tonight's shooting stars
it shines in the northern constellation Lyra.
