NGC 6888 : An XXL Croissant

I had already shot NGC 6888 in December 2024 with the Fra400 during my vacation at Casa Astro (La Palma, Spain).

This time I wanted to try it with a larger focal length for more details.

NGC6888 taken in La Palma with Fra400 - December 2024

The Crescent Nebula (NGC 6888) is an emission nebula located in the constellation Cygnus, approximately 5,000 light-years away.

This envelope of matter is produced by a very special type of star, a "Wolf-Rayet star," named after the two astronomers from the Paris Observatory who discovered this type of star using spectroscopy in 1867.

Wolf-Rayet (WR) stars are hot stars, probably born from stars of spectral types O and B (i.e., the hottest and most massive stars in existence) that have just left the main sequence and are therefore entering the final stages of their lives.

Wolf-Rayet stars involve stars with a mass greater than at least 15, or even 25, times the solar mass (depending on metallicity) ; and current research tends to demonstrate that these inevitably end in a supernova.

When these stars leave their main sequence, several types of reactions involving the fusion of different elements ( hydrogen and helium in particular) are at work simultaneously in the core and in different layers of the star. This results in instability (collapse and then rebound of the layers) that leads to the very high-speed expulsion of the material surrounding the core in the form of a stellar wind.

Researchers estimate that WR-136 is expected to explode as a supernova in the "near" future (on a universe scale), within 100,000 to 1 million years.

Set up

Celestron C8 Telescope full focal length on EQ6 R Pro Mount
ASI533 MC Pro camera for imaging
ASI220 mini camera for guiding via Off Axis Guider Celstron
Optolong L Quad
Control via ASIAIR PLUS
Gain (ISO) : 101
Camera cooling : -10°C

Preprocessing and Processing with Pixinsight


The session

NGC 6888 was taken in August 19th 2025
36 images of 5 minutes each
Total integration : 3 hours.

Pretty cool guiding at 0.30”



Single image, I thought to myself... It's going to be complicated… Very few details...

The process with PixInsight

WBPP Stack
Dynamic Crop
Gradient Correction
Image Solver
SPCC
BlurX Terminator in normal mode
Fast stretch : Triangle from STF to histogram transformation
SNCR at 0.71
NoiseX Terminator at 0.60
StarXTerminator to remove temporarily the stars
Curve on the starless then RGBK in S curve and slight saturation
Range selection then HDR Multiscale Transform at 6
Slight general saturation
Reintegration of the stars with PixelMath
Slight NoiseX Terminator

The Final Image : A croissant that fits with a shoehorn !

Astrometry : Annotated image

Clear Sky !

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