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Comet PANSTARRS (C/2014 S2) - with processing notes, 


            Tony Cook
Comet PANSTARRS (C/2014 S2) - with processing notes
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Comet PANSTARRS (C/2014 S2) - with processing notes

Technical card

Imaging telescopes or lenses: ASA N10 astrograph

Imaging cameras: canon 450D

Mounts: 10 Micron 1000 HPS

Focal reducers: ASA 3" Wynne Corrector 0.95x

Software: Russle Croman GradientXTerminator  ·  Noel Carbonni Astrotools  ·  Mike Unsold Images Plus  ·  Photoshop CS 2

Dates:Oct. 2, 2015

Frames: 30x300" ISO800

Integration: 2.5 hours

Darks: ~36

Flats: ~25

Flat darks: ~25

Avg. Moon age: 19.72 days

Avg. Moon phase: 74.66%

Mean SQM: 20.42

Temperature: 6.00

Basic astrometry details job: 3436724

RA center: 2h 50' 10"

DEC center: +87° 10' 19"

Pixel scale: 1.190 arcsec/pixel

Orientation: 275.656 degrees

Field radius: 0.756 degrees

Resolution: 3910x2372

Locations: Dark Sky Site, Kirby Malzeard, North Yorkshire, United Kingdom



Comet C/2014 S2 unexpectedly brightened in late September 2015 to 10th magnitude. This image was captured in a 2 hour dark sky window between the end of twilight and moon rise on 2nd October 2015.

The comet is ~ 3 degrees from the north celestial pole on this date and appears in front of the very faint Polaris Nebula of which only hints are visible in this image (The Polaris Nebula is an IFN - integrated flux nebula - dust high over the our galactic disk which is both reflecting the light from all the stars in our galaxy and glowing a faint deep red due to absorption of near infra-red and re-radiation into the infra and deep red parts of the spectrum)

The comet has developed a noticeable green coma from sun light trapped and fluoresced by acetylene di-radicals formed in the coma gasses surrounding the comet nucleus. It also sports a short dust tail.


Stacking was done in deep Sky Stacker (using the time stamp position interpolation method for comet alignment). Digital Development Processing in Images Plus and filtering and image treatment in Photoshop.

The stars only image was processed using an adaptation of the Hubl method. The adaption was required to preserved the faint IFN. The calibrated RAW star aligned images were stacked using kappa sigma (sigma 1.15, 10 iterations) image combination. The result image was duplicated into S and T. T is processed using the Hubl method - first treat T with the GradientXterminator filter (Russel Croman plugin) to reduce the comet artefact as much as possible then further duplicate image T into A & B then B has applied the following filters - Dust & Scratches filter [radius 15, threshold 6], Gaussian blur [radius 10] and then subtract B from A with an offset equal to the mean sky background of A to create image T' - now containing just background sky. A deep feathered selection from T' carefully extracting the area containing the residual comet artefact is placed over image S - this is now the stars-only image with preserved IFN and this is further processed to reduce high frequency noise and improve star colour to give final stars-only image S'.

The comet only image is created by median stacking all the calibrated RAW images aligned on comet found in the same reference frame used for star alignment to create image C (this contains the isolated comet and a lot of star residual artefacts). C is duplicated to create images C & D. D then uses a large radius clone stamp tool (radius slightly larger than the comet coma) to carefully stamp out the comet to leave only background. D is then Gaussian blurred (radius 10) and subtracted from C with an offset of 0 to give C' - a very dark image containing only the comet.

C' (processed comet-only) is then layered over S' (processed stars-only) using screen blending. Finally the black point is set. The use of the same reference frame in the S and C images ensures that the processed images S' and C' are correctly aligned in the screen blending step.


Version B: Lowered the black point to make the very faint IFN a little more visible. There was a lot of dead space at the black end of the histogram due to the screen blending mix of the comet only and star only images.



Tony Cook
License: Attribution-NonCommercial-NoDerivs Creative Commons


  • Final
    Comet PANSTARRS (C/2014 S2) - with processing notes, 


            Tony Cook

Sky plot

Sky plot


Comet PANSTARRS (C/2014 S2) - with processing notes, 


            Tony Cook

In these public groups

Cloudy Nights
Comets Imaging