"NGC 6888, also known as the Crescent Nebula, is a about 25 light-years across blown by winds from its central, bright, massive star....Visible within the nebula, NGC 6888's central star is classified as a Wolf-Rayet star (WR 136). The star is shedding its outer envelope in a strong stellar wind, ejecting the equivalent of the Sun's mass every 10,000 years. The nebula's complex structures are likely the result of this strong wind interacting with material ejected in an earlier phase. Burning fuel at a prodigious rate and near the end of its stellar life this star should ultimately go out with a bang in a spectacular supernova explosion. Found in the nebula rich constellation Cygnus, NGC 6888 is about 5,000 light-years away." https://science.nasa.gov/ngc-6888-crescent-nebula

"Discovered by William Herschel in 1792, the Crescent Nebula is the result of a type of star known as a Wolf-Rayet, which are massive stellar objects that are ageing and losing mass at an incredibly high rate.
That's certainly the case with this Wolf Rayet: the star is shedding its outer layers into space at a rate equivalent to the mass of the Sun about every 10,000 years.
This violent and rapid ejection has produced a dense shell of scorching hot material that gives the nebula its shape, while the complex structures seen within the bubble are likely the result of stellar winds colliding and interacting with older material ejected by the star long ago.
It is thought that the star at the centre of the Crescent Nebula - known as WR 136 - will eventually end its life in a dramatic stellar explosion known as a supernova."
https://www.skyatnightmagazine.com/astrophotography/nebulae/crescent-nebula/

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Like every project, this one has represented a good challenge.

Maurizio collected the data in August 2020/2021 under a windy conditions and is the reason he used relatively short times and high ISO to counteract it in the place where he made the images near the Foreste Casentinesi National Park, Cesena in central Italy. Beside that the fact that the IOptron mount with the Newton was close to the limit payload so any wind will interfere/damage the image session.

The histogram of all the frames of the Canon R and Ra and the Enhance filter are very shifted to the left, the base of most touches the histogram blackpoint and the L-Pro not so much but it is located in between 1/4 of the histogram as well.

I ended up doing a lot of stack tests, for each Canon R- LPro session and  the R- Enhance filter, and for the ones taken with the Canon Ra. The results of the Enhance were inadequate, with a lot of background noise that I could not solve in any way... but it was used as the basis of the gas body nebulosity that is around the Crescent. For all the stacks was used the best 90% of all frames.

The DSS stacks from the Ra sessions were promising, but the ones from Siril, with the usual parameters (Winsorized Sigma Clipping) that I always use when doing a second stack with the best frames under FWHM and roundness, for some reason they were not good, and showed almost no sign of the Crescent as of the surrounding cloud gas.

I decided not to do more tests with other parameters in Siril after seeing the results (I was tired too). In any case, I used the Siril stack to combine it with the L-Pro since the stars had a beautiful definition and the starless version was also incorporated in a small percentage in the final mix of the image.

Alsowas done the extraction of OIII and Ha from the Ra sessions (which by the way were done without a filter ) and they were combined as HOO and I didn't get a satisfactory result either...

Lastly I did a stack 2 drizzle in DSS where I was finally able to get better details of both the Crescent and the surrounding cloud cover.

Then a final mix was made where basically the Ra sessions contributed almost 78% of the image, the Enhance 12% and the L-Pro and Siril Ra stars the rest. What I did notice is that the  [OIII] around the Crescent is well spread as much the Ha in the nebulosity area.

Unfortunately we was unable to catch the little Soap Bubble Nebula, PN G75.5+1.7.

Crescent Nebula is definitely a difficult DSO and needs dedicated data from both Ha and OIII done right and we would like to do again with better data, hopefully so.

Thank you for visiting us and see our work, have all Clear Skies!!

Processed June 2022