Hemisphere:  Northern
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ARP 273 : UGC1810  and UGC1013, 


            Jonathan W MacCollum
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ARP 273 : UGC1810 and UGC1013

Technical card

Imaging telescopes or lenses: Orion 203/1000 f/4.9

Imaging cameras: ZWO ASI183MM-pro

Mounts: Celestron CGEM

Guiding telescopes or lenses: ZWO OAG

Guiding cameras: ZWO ASI 178MM

Software: PixInsight PinInsight 1.8.5  ·  Isbeorn N.I.N.A.  ·  PHD 2

Filters: Astrodon LRGB Tru-Balance I-Series Gen B  ·  Astrodon LRGB Tru-Balance I-Series Gen G  ·  Astrodon LRGB Tru-Balance I-Series Gen R  ·  Astrodon LRGB Tru-Balance I-Series Gen L

Accessory: Skywatcher 2" Coma Corrector f/4  ·  ZWO EFW 8 EFW 8x1.25" filter wheel

Dates:Nov. 25, 2019

Frames: 97x120"

Integration: 3.2 hours

Avg. Moon age: 28.30 days

Avg. Moon phase: 1.70%

Astrometry.net job: 3078470

RA center: 2h 21' 30"

DEC center: +39° 24' 50"

Pixel scale: 0.498 arcsec/pixel

Orientation: -96.887 degrees

Field radius: 0.254 degrees

Resolution: 3144x1910

Data source: Backyard


In the center of this image lies two galaxies that are interacting. The one on top is quite a bit bigger than the one on the bottom right and in the past the one on the bottom seemed to have run through the middle of the top one forming a bridge between the two. Their interaction has left an interesting spiral pattern in the top galaxy from the tidal forces involved at this galactic scale.

I came across this target last night while wrapping up acquisition on the Heart Nebula when I stumbled upon sky-watcher (johny)'s latest image of ARP 273 (UGC1810 - 1813) I was so transfixed by how exciting this target looked in his image I immediately pulled it up in my atlas and saw it was still in a great part of the sky to image (straight up!) so I just had to switch gears and check it out for myself. When the first frame came in I knew my plans for the night were immediately changed, and so I set up a sequence in N.I.N.A to let it acquire data until it reaches the meridian. I did a quick stack of the while I moved to my origionally planned target (LBN777) and the initial stack looked like an almost-finished work by itself. So I decided to go ahead and follow it down the other side of the meridian to see what the rest of the night could yield, and then gave myself a challenge... If Johny could create such a great image with only 4 hours of data at f/4 maybe, given seeing conditions were fairly decent tonight (and cgem was actually behaving for once) could I come up with a half-decent result. In the end I ended up with 40 minutes of each R, G, and B filters and an hour 20 minutes of luminance and this morning sat down to see what I could do.

Thanks Johny for the inspiration!


Orion 8in F4.9 1000mm Newtonian Reflector

Flocked / Primary mirror replaced due to turned-down-edge

Skywatcher F4 Aplanatic Coma Corrector

Astrodon I Series L, R, G, B broadband filters

ASI183mm Pro cooled to -15C

Celestron CGEM Mount

Self tuned / hacks to get guiding stable include:

Intentional offset polar alignment so dec always pulses in one direction

Balance "west" heavy (rather than the recommended east) so that the ota "falls" onto the gear teeth rather than get "lifted"

Factor Reset hand-controller daily (to prevent cgem from being possessed and forgetting where the meridian is on subsequent night)

Dither in RA only

Red: 20x2min

Green: 21x2min

Blue: 20x2min

Lum: 37x2min

The resulting image is a combination of the following steps:

Inspected all 101 subs for bad images with Blink, discarding 3 (keeping 97)

Calibrated all subs with their corresponding master flat and master dark

Used subframe selector to weight all subs together using the following formula:


+ 20*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))

+ 15*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)

+ 20*(Stars-StarsMin)/(StarsMax-StarsMin))

+ 30

Selected the best sub from subframe and blink to use as a reference frame in stacking

Created a super luminance by integrating all 97 frames together

Integrated all Red frames together, Blue frames together and Green frames together to create masters for each color

Cropped the stacking edges of the integrated masters

Combined the Red, Green and Blue masters to create a color RGB image

Superluminance Processing:

Automatic Background Extractor

Function degree 1 with normalization

Independently produce a noise reduced image and a sharpened image

Noise Reduction was done using TGV Denoise with a low contrast mask and an autostretched local support and MMT with a very protective luminance mask

Deconvolution was done on a separate copy of the luminance with

No deringing

wavelet regularization with 5 layers and strong but reducing amounts/thresholds

A starmask was created from the Noise Reduction copy to replace the stars with the origional superluminance, eliminating the ringing artifacts from deconvolution as similarly documented by /u/OkeWoke

The noise reduced copy and the sharpened copy were combined using a luminance-based mask where the high-signal areas were filled in from the deconvolution copy and the low-signal areas were filled in from the noise reduction copy:

Two rounds of Masked Stretch was used with no clipping and a background reference created from 5 preview windows and the Preview Aggregator script. Between each round the histogram transformation tool was used to bring the tail in without clipping and gentle noise reduction was performed in between the two stretches.

RGB Processing:

Automatic Background Extractor

Function degree 1 with normalization

Background Neutralization using 5 preview windows and the Preview Aggregator script as the background reference

Color Calibration using Photometric Color Calibration using the Average Spiral Galaxy as the white reference

Noise Reduction using TGV Denoise with a low contrast mask and an autostretched local support

Noise Reduction using MMT with a very protective luminance mask

Repair the saturated star cores with the HSV Repaired Separation script

Arcsinh Stretch and Histogram Stretch

SCNR Green on the background with a luminance mask

Noise reduction with ACDNR to smooth out the background of the color image

Power of Inverted Pixels and Curves with a luminance mask to brighten and adjust saturation of the high-signal areas

Star reduction using the Morphological Selection

The super luminance and the RGB image were then combined using the Channel Combination tool in CIE L*A*B mode.
A final gentle s-curve and saturation curve was applied at the end to produce the final image.



Jonathan W MacCollum
License: Attribution-NoDerivs Creative Commons


  • Final
    ARP 273 : UGC1810  and UGC1013, 


            Jonathan W MacCollum
  • ARP 273 : UGC1810  and UGC1013, 


            Jonathan W MacCollum


Description: Full Frame

Sky plot

Sky plot


ARP 273 : UGC1810  and UGC1013, 


            Jonathan W MacCollum