APOD: 2022 December 20 - Thors Helmet

Good morning, Rallypoint, and welcome to the December 20th edition of Astronomy Picture of the Day (APOD): "Thor's Helmet." A popular target for multiple APOD contributors, NGC 2359 (aka Thor's Helmet) is located 11,000 light years away from Earth near the constellation Canis Major (Big Dog). This image combines visible light and data collected from using narrowband filters to provide both natural stars and the whispy structures of the nebula itself. The last appearance of Thor's Helmet was in July 2021.

We've seen the use of narrowband filters in previous APODs, but what they actually are isn't always well described. Narrowband filters permit the detection of different elements based on emission line wavelengths of their electromagnetic spectra: ionized hydrogen (Hα; 656nm) sulfur (S-II; 672nm), and oxygen (O-III; 496nm). I'm guessing on the color palette...hydrogen: green, sulfur: red, and oxygen: blue. A Wolf-Rayet star sits near the center of the helmet, and is expected to supernova in a few thousand years.