More Backyard Astronomy 7/15/2020. This is my work in progress photograph of the Crescent Nebula known as NGC6888. This object is an emission nebula, a cloud of hot gas glowing in the void of space excited by ultra violet light emitted from the nearby stars. An emission nebula is like a neon light just hanging there in the void of space. NGC6888 is located in the constellation Cygnus, the Northern Cross, about 5,000 light-years away from Earth. It was discovered by William Herschel way back in 1792.

This nebula was formed when a smaller star cooled and then began to swell into a red giant star back around 250,000 to 400,000 years ago. The pathway from a cloud of gas forming into a star and moving on to form a blue star and red star, etc. is called the Main Sequence. Eventually a main sequence star becomes a Red Giant star like our well known Betelgeuse in the Constellation Orion.

As this star was forming into its red giant stage it was exposed to a fast stellar wind blowing from a Wolf-Rayet star, which is a special type of star that is extremely hot and massive. This hot and fast moving wind began colliding with and energizing the slower moving wind ejected from the ever growing red star. The result of the collision of winds 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 like the summer days in Texas and Alabama.

The shell can be seen in my photograph and reminds me of the bubbles I blew as a kid from my one cent piece of Fleer Bubblegum (the best part of Fleer gum was the neatly folded and great smelling sheet of wax paper with a comic printed on it).

As the shell or bubble continues being formed by layers of gas peeling off the red star, eventually the bubble will pop and there will be a gigantic explosion. We call these explosions a nova or super nova. Maybe the nova already happened and we won't know for another 5,000 years as it will take that long for the light to reach us.

The Cresent Nebula is a rather faint object and I have stacked 299 one minute exposures so far to just see this much of the crescent in my photograph. Some astronomers see a Euro sign shape which makes them call NGC6888 the "Euro Sign Nebula".

I like the colors of this nebula. The light blue shroud covering the nebula is made of oxygen atoms. The red clouds are composed of hydrogen and sulfur. This photograph is comprised of exposures I have made on July 11, 12, 13th, and the 14th. I was hoping to pick up about a hundred exposures last night, but clouds came in and I was lucky to get about 60 one minute exposures. I will keep at this project and keep posting any significant results. Thanks for looking. Clear skies to you. Ken Adler