NGC 2359, Thor's Helmet, in Canis Major, is a bubble-like complex of emission nebulosity that is illuminated by a hot Wolf-Rayet star.

The nebula formed from the winds of the massive central star that the sweep through the surrounding molecular cloud. It gets its blue-green color from oxygen atoms emitting light in the gas that makes up the nebula.

Wolf-Rayet stars are extremely hot young stars that are believed to be in a pre-supernova stage of their stellar lifetime. Other nebulae around Wolf-Rayet stars are the NGC 7635, the Bubble Nebula and NGC 6888, the Crescent Nebula.

The nebulae that form around Wolf-Rayet stars are very different than planetary nebula like M57, the Ring Nebula.

Wolf-Rayet nebulae form around massive hot young O or B type stars that will explode in a supernova.

Planetary nebula form around old stars that are not massive enough to go supernova. These old stars at the center of planetary nebula have shed their outer layers during their red-giant phase and this material is illuminated by the white dwarf that remains.

NGC 2359 is 30 light-years wide and located 15,000 light-years away.

NGC 2359 was discovered by William Herschel in 1785.

North is to the top in the above image.

NGC 2359 Catalogs: NGC 2359, LBN 1041, Sh2-298 Common Name: Thor's Helmet, Duck Nebula Object Type: Emission nebula Size: 9' x 6' Constellation: Canis Major Image Field Centered At: RA: 07h 18m 31s Dec: -13° 13' 20"