Comet Nishimura on September 2, 2023

Having learned how to process comets thanks to the excellent videos by Adam Block, I went back and finished processing my first image of Comet Nishimura from September 2, 2023.  That morning we got up at 3:30 AM and drove over to Bacliff, Texas to get a good view to the East, and got set up.  I found the comet, started taking pictures, and enjoyed watching the sunrise.  As the sun rose over the flat water, we saw dolphins arcing out of the water – one of my favorite sights on the Texas Gulf Coast.  

Because the September 2 images involved a compact comet with not much tail and a short range of locations and a rapidly brightening background, I modified the excellent instructions from Adam Block as follows:

Register and process images as normal (noting the reference image), then removing the comet using a circular mask that covered the first and last locations and PixelMath.  I could get away with this because the comet didn’t have a large tail and hadn’t moved very far and there were no visible stars in the masked-out region.  In this case, I integrated unweighted; if I were doing it again, I would use the weighting I determined below.

Run SubframeSelector to determine what parameter to weight the images with – PSF SNR seemed to best reflect the lower quality due to the sky brightening in the last images.

Run CometAlignment on the debayerd data to get comet-aligned images.  Use PixelMath to make a mask to mask the comet core.  Run StarXterminator to generate comet-only images.  Integrate the images using PSF SNR weighting.  Then post-process as normal.  I could barely see the comet tail in these images and I tried a variety of stretches to try to pull it out.  I ended up using STF and Histogram Transfer plus Curves.  

Finally, put the stars image and the comet image back together using PixelMath.

Whew!  Comet processing is a lot more complicated than galaxies and nebulae.  Fun to see something new in the sky, though.

Camera geek info:

• Canon EOS 60D in manual mode, 60 second exposures, ISO 800 
• Williams Optics Zenith Star 73 III APO telescope
• Williams Optics Flat 73A
• SkyTech 2” LPRO-MAX CCD Filter
• iOptron CEM40
• Bacliff, Texas Bortle 6 suburban skies

Frames:

• 24 60 second lights
• 30 0.03 second flats
• 30 0.03 second flat darks
• 30 60 second darks

Processing geek info:

• PixInsight
• NoiseXterminator
• StarXTerminator