Explanation: This helmet-shaped cosmic cloud with wing-like appendages
is popularly called Thor's Helmet. Heroically sized even for a
Norse god, Thor's Helmet
is about 30 light-years across. In fact, the helmet is more like
an interstellar bubble, blown as a fast wind from the
bright, massive star near the bubble's center sweeps through a surrounding
molecular cloud. Known as a
Wolf-Rayet
star, the central star is an extremely hot giant thought to be in a brief,
pre-
supernova stage of evolution. Cataloged as NGC
2359, the
nebula is located about 15,000 light-years
away in the constellation
Canis Major. The
sharp image, made
using broadband and narrowband filters, captures striking details of
the nebula's
filamentary structures. It shows off a blue-green color from strong emission
due
to oxygen atoms in the glowing gas.
