Tuesday, February 20th, 2018

Crescent Nebula again


I say “again” because I have been worrying this poor nebula to death for the past month or so. I promised myself that after I had wrung all I could out of the hours of data I have collected, I would write a little essay about the Crescent Nebula. Maybe this is it and maybe it is not. I’m getting tired of looking at it.

The nebula is a shell of gas that is being energized by the strong stellar wind from the Wolf-Rayet star WR 136, the bright star at the center of the nebula. It is located in the constellation of Cygnus, the Swan. Wolf-Rayet stars are very hot, massive stars that are blowing off their outer layers.

Crescent Nebula

The all-knowing Wikipedia says this about the nebula

The Crescent Nebula (also known as NGC 6888, Caldwell 27, Sharpless 105) is an emission nebula in the constellation Cygnus, about 5000 light years away. It is formed by the fast stellar wind from the Wolf-Rayet star WR 136 (HD 192163) colliding with and energizing the slower moving wind ejected by the star when it became a red giant around 400,000 years ago. The result of the collision is a shell and two shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray-emitting temperatures.

That adds a little more information. And from Waid Observatory, Denton, Texas

NGC 6888 (The Crescent Nebula)

NGC 6888 is located approximately 4,700 light years from earth and is known as the Crescent Nebula because of its distinctive shape. Technically it is classified as a Wolf-Rayet nebula. Such a nebula is formed when a very hot, massive star ejects its outer layers in a strong stellar wind. In the case of the Crescent Nebula the star responsible (WR 136) is the bright star in the center of the image above. As the star ages it begins to shrink and grow much hotter. Its stellar wind becomes more rarefied but much faster. This fast stellar wind then collides with the older ejected gas and pushes it into a relative dense bubble. The radiation from the hot central star excites the gas, principally hydrogen, causing it to shine in the red spectrum typical of an emission nebula. … WR 136 is in the final stages of its stellar life and is estimated to explode in a supernova event within the next million years

Creating this image is an educational project for me, and I will say right off that I still have a lot to learn. The perfectionist in me says that I really should re-gather some of my data, try different emission-line images in Hydrogen-alpha (red), Oxygen [O III] (blue) and Sulfur [S II] (yellow) to achieve better color, and go to work on some excessive star halos. If you are wondering about this, click on the image to blow it up and see for yourself. But for a guy who couldn’t even pronounce Photoshop a couple months ago, it ain’t too bad.

Dave, just glad that he doesn’t have to go outdoors to see his stars.


2 Responses to “Crescent Nebula again”
  1. Tom says:

    Gotta hand it to you Dave it is nice. Can’t wait for the next project you start on!

  2. Dave says:

    Thanks, Tom. I’ve been gathering data in between New Mexico storms (it isn’t supposed to be stormy there this time of year). But sooner or later I will gather color information to go with my very good luminance data. Maybe I’ll go ahead and post about it with an image one of these days,

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