M57: The Ring
Nebula
From
NASA’s Astronomy Picture of the Day
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 our own perspective,
though.
The recent mapping of the expanding nebula's 3-D structure, based in part on this clear Hubble image, indicates that 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, once 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.
