This object, also known as Sharpless 2-298 and Gum 4, is an emission nebula located 15,000 light years away in the constellation of Canis Major at a declination of -13 degrees. This nebula spans 40 arc-minutes in our apparent view, which corresponds to a width of 180 light years.
This is one of my favorite deep sky objects. It has many nicknames, including Thor’s Helmet, Flying Eye, and Duck Head Nebula. The nicknames should have stopped at Thor’s Helmet.
Determining the distance to these nebulae is important but very difficult. Particularly for this one. I have found distance estimates for this nebula, all from reliable sources, that range from 1500 to 15,000 light years. I am still not confident in the final estimate (15,000 light years) that I used here.
The central star here is the Wolf-Rayet star WR7, the bright star seen near the center of the bubble. These are massive stars which have high temperatures and which are highly luminous. They also have a high rate of mass loss as they expel outer layers towards the end of their lives. These stars result in some of the
prettiest nebulae in the universe.
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