Explanation:
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.
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