Thor's Helmet
Thor's Helmet, also known as NGC 2359, is an emission nebula located approximately 15,000 light-years away in the constellation Canis Major. Spanning about 30 light-years, this helmet-shaped cosmic cloud is formed by the powerful stellar winds from a central Wolf-Rayet star, which sculpt the surrounding molecular cloud into a bubble-like structure.
Source: apod.nasa.gov
APODs including "Thor's Helmet"
Thor's Helmet (NGC 2359) and Planetary Nebula
12/03/2009
At the right, Thor's Helmet (NGC 2359) seems to gaze across a lovely star field. The broad skyscape itself covers about 1.5 degrees or 3 full moons toward the constellation Canis Major. A close look at the lower left corner of the image might identify the object of the cosmic stare as a faint, round nebula. Heroically sized even for a Norse god, Thor's Helmet is about 30 light-years across. 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. In contrast, the faint, round nebula is a planetary nebula, the gaseous shroud of a dying lower mass star. The distance to Thor's Helmet is estimated to be about 15,000 light-years.