NGC 2359 (also known as Thor's Helmet) is an emission nebula
in the constellation Canis Major. The nebula is approximately
3,670 parsecs (11.96 thousand light years) away and 30 light-years
in size. The central star is the Wolf-Rayet star WR7, an extremely
hot star thought to be in a brief pre-supernova stage of evolution.
It is similar in nature to the Bubble Nebula, but interactions with
a nearby large molecular cloud are thought to have contributed to
the more complex shape and curved bow-shock structure of Thor's Helmet.

It is also catalogued as Sharpless 2-298 and Gum 4.

The nebula has an overall bubble shape, but with complex filamentary
structures. The nebula contains several hundred solar masses of ionised
material, plus several thousand more of unionised gas. It is largely
interstellar material swept up by winds from the central star, although
some material does appear to be enriched with the products of fusion
and is likely to come directly from the star. The expansion rate of
different portions of the nebula varies from 10km/s to at least 30km/s,
leading to age estimates of 78,500 - 236,000 years. The nebula has been
studied at radio and x-ray wavelengths, but it is still unclear whether
it was produced at the class O main sequence stage of development, as a
red supergiant, luminous blue variable, or mainly as a Wolf-Rayet star.

NGC 2361 is a bright knot of nebulosity on one edge of the central ring
of NGC 2359.