This is the fourth session that Maurizio did on the night of March 14 in the Apennines, a place called La Faggia at 740 masl. and it's this comet's turn C2021 S3 PanSTARSS. At that time the comet was crossing the Serpens Cauda Constellation. When I reviewed the raw frames it was a small shock to observe the myriads of stars found in the Milky Way field.

This led me to have another type of approach to process this session since it was essential to isolate the comet from a background so rich in stars. Fortunately, in previous days I had seen a video by Rich   on how to process comets with the latest version of Siril 1.2.1, where in the workflow the starless-comet stack is created, etc., so I took advantage of the opportunity to upgrade the program and follow the steps for processing.

As is almost always the case, not everything always flows smoothly. Once the initial preprocess stack is done, as explained in the video, the pp_light sequence is taken  for to do the rest of the workflow steps.  Result? A starless stack only-comet with the entire head distorted... I reviewed the comet-starless files produced by Siril using StarNetI2 which is incorporated into their program and they were wonderful, the comet was perfectly isolated, a smooth background, a beautiful comet, with its tail raised aside comically. I did not understand.

I then decided to use Siril's comet-starless .fit files and convert them to .tif. Since there were only 28 frames, I gathered the sequence into 4 groups of 7 and exported them in Ps by manually stacking each group. It took some time but it was easy. Then I made the final stack with the previous four resulting manual stacks.

For the stars part, I made a normal stack in DSS, then isolating the comet-trail and obtaining the stars base without the comet. Really impressive to see how many stars there are in that Milky Way region.

Note:  in the Siril comet workflow when StarNet2 produces the comet-starless frames, it also makes stars-only frames through a mask, then both results are stacked apart and are joined under the Star Processing-Star Recomposition tool for the final image. Due to personal preference I do not use Siril's stars-only stack, I prefer to use the stars base that I always make and the texture result that DSS gives me.

However, I investigated why I got that bad result in Siril's comet-only stack and reviewing the frames I noticed that the comet in the sequence 'jumped', in one frame is above, another a little lower and so on...I deduced that the problem was having chosen the sequence prior to registration (pp_light) since the stars in that stage are not aligned, but in the registration sequence 'r_pp_light' they are and therefore the comet has a linear path.

I redid the whole process taken the 'r_pp_light' sequence and Siril's comet-only stack was perfect. This result was combined with what I had done manually and NoiseXterminator was applied, then the stars base was incorporated and in CamRaw, color, dehaze, clarity and white and a soft S curve were applied, obtaining the image that you see. In Revision B is a crop of the fullframe image.

Maurizio is very glad for be able to catch four comets that night,  which two of them is the first time image by him and now are part of our repertory.

With this work this cycle of comets closes for the moment, although Maurizio did other sessions after to the comet Tsuchinsan, I will dedicate to finishing some nebulae that I left halfway before!!

Thank you for visiting us and everyone have Clear Skies

Processed April 2024.

https://twitter.com/AstroOtus/status/1786024923330166944