In Canis Major, nearly 12,000 light years from Earth, lies an emission nebula that always makes me think of a particular comic book character.  NGC 2359 is 30 light years across, and is colloquially known as Thor’s Helmet. The complex structure of Thor’s helmet consists of bubbles and filaments, and is due to a series of bursts from the massive star HD 56925.  This star is a rare Wolf-Rayet star, which consistently expels its outer layers of gas at high velocities, and is characterized by its very high temperature. The blue bubble in the above image is a result of...