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Contains:  M 51, NGC 5194, NGC 5195, Whirlpool galaxy
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M51 Whirlpool Galaxy, 


            Michael Southam

M51 Whirlpool Galaxy

Technical card

Dates:Feb. 20, 2015

Frames: 115x45"

Integration: 1.4 hours

Avg. Moon age: 1.75 days

Avg. Moon phase: 3.41%

Basic astrometry details job: None

RA center: 13h 29' 52"

DEC center: +47° 11' 45"

Orientation: 86.708 degrees

Field radius: 0.229 degrees

Resolution: 3119x2261

Locations: Rolnick Observatory, Westport, Connecticut, United States


This image sums up how much I’ve learnt about astro imaging and processing in the last year.

M51 was one of my first targets last year and the result was less than pleasing. I made the background far too dark and had great difficulty highlighting the bridge. The problem essentially was that I hadn’t heard of PixInsight. I also took far too few subs. Both issues have been rectified here.

I took 100 x 45 second subs and 15 darks. I did have significant difficulty stacking though. On the first attempt I got the old ‘cannot integrate less than 3 frames’ In short what that means is that PI couldn’t register the frames on account of not finding stars. The reason for this took me 3 more attempts to resolve which when each stack takes many hours, means 3 more days. I did search the PI forums for the answer which led me to adjust the Image Registration Clamping Threshold for the second attempt at stacking to no avail. For attempt 3 I remembered that noise had been the issue last time this happened so I tried upping the Noise Reduction setting from 0 to 1. I thought this had worked but when I looked at the script closely, I noticed that only 17 of the 100 frames had been successfully integrated after 7 hours of processing. I upped the Noise Reduction to 4 and managed 80 integrated frames after 10 hours of processing. I settled for that and the result was close to the final image you see here. A few minutes removing the gradient and adjusting the histogram in PI and I moved the image over to PhotoShop. There I adjusted Levels, Curves, Color and Contrast and that was all it need.

This is my favorite image to date for a few reasons. One reason being the improvement from my last attempt at M51 and the second because I ended up with a very natural looking image with very little manual adjustment.



Michael Southam
License: Attribution-NonCommercial-ShareAlike Creative Commons


  • M51 Whirlpool Galaxy, 


            Michael Southam
  • Final
    M51 Whirlpool Galaxy, 


            Michael Southam

Sky plot

Sky plot


M51 Whirlpool Galaxy, 


            Michael Southam

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