Thor’s Helmet, or NGC 2359 is an emission nebula located in the constellation of Canis Major.
The nebula is also known as Sharpless 2-298 and Gum 4.
Containing several hundred solar masses of ionised material and several thousand of unionised gas, the nebulas material is mostly swept up by interstellar winds from it’s central star.
The expansion rate of the nebula varies in certain locations from 10km/s to 30km/s. Thor’s Helmet is expected to be somewhere from 78,500 years old to 236,000 years old.