Thor's Emerald Helmet

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 actually 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 captures striking details of the nebula's filamentary structures and also records an almost emerald color from strong emission due to oxygen atoms in the glowing gas.