The crescent nebula is in the constellation of Cygnus about 5000 light years away. It is likely formed from the interaction of energetic solar wind of the Wolf-Rayet star WR 136 with slower moving material ejected at a previous stage. It is near the end of its life and is expected eventually to go super nova.

Technical Details

This image was taken at Brooks Memorial State Park in Goldendale Washington at a Seattle Astronomical Society gathering in 2019.

Total Integration time: 5 hours and 20 minutes, all taken at gain 300 offset 20, broken down as so:

Ha - 2 Hours (of 2 minute exposures 1x1 binning)

SII - 2 Hours (of 2 minute exposures 3x3 binning)

Red - 20 minutes (of 30 second exposures 3x3 binning)

Green - 20 minutes (of 30 second exposures 3x3 binning)

Blue - 40 minutes (of 30 second exposures 3x3 binning)

I used Astro Pixel Processor to stack these images using dark and bias calibration only (no flats). For the 3x3 binned images I found that scaling to 3 at integration step and using drizzle produced the best results. The resultant stacks can then be aligned at the same scale.

During processing this I created two separate images in pixinsight and merged them. Here is a description of each:

1. Bi-Color Narrowband image made up of Ha and OIII. I used StarNet to remove the stars from the narrowband bicolor image and used Ha for red, OIII for blue and a synthetic green made up of a combination of the two.

2. RGB image made up of a stack of fairly short exposures because I was just exposing for stars to get star color. The nebula itself was very faint in the RGB star image.

The combined image is a merge of the two using some pixel math expressions and processed further both in PI and Photoshop.

Lessons learned:

I should not have binned the OIII at 3x3. I had to use Ha for Luminance and while I had the OIII for color there were some areas which did not have the correct value despite having the right color which got lost (namely the bubble extending past the Ha part of the image). If I do this again I will shoot OIII at 1x1 and allocate about 50% more total integration time to the OIII then the much brighter (higher signal) Ha.