Except for the rings
Nebula (M57) is probably the most famous celestial band.
Its classic appearance is
understood to be due to our own perspective, though.
The recent mapping of the
3-D structure, based in part on
this clear Hubble image,
the nebula is a relatively dense, donut-like ring wrapped
around the middle of a football-shaped cloud of glowing gas.
The view from planet Earth looks down the long axis of the football,
face-on to the ring.
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,
sun-like star, now a tiny pinprick of light
seen at the nebula's center.
Intense ultraviolet light from the hot central star
ionizes atoms in the gas.
In the picture, the blue color in the center is
ionized helium, the cyan color of
the inner ring is the glow of hydrogen and oxygen,
and the reddish color of the outer ring is from nitrogen and sulfur.
The Ring Nebula is about one light-year
across and 2,000 light-years away.
ESA, and the
ESA / Hubble Collaboration