NGC 2359 (also known as Thor's Helmet) is an emission nebula[3] in the constellation Canis Major.

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.

The nebula contains several hundred solar masses of ionised material, plus several thousand more of unionised gas.

[5] The expansion rate of different portions of the nebula varies from 10 km/s to at least 30 km/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.