Sunday, 26 April 2020

M51 - Snatched From The Jaws Of Defeat

M51 - Snatched From The Jaws Of Defeat

Welcome to the latest in this series of catch up blog posts.  I've managed to cram in so much astronomy this Spring that the topics I feel that are worthy enough to write a few lines about, are stacking up!  So, let's continue through this backlog and get on with today's post.
This post hails back from a week ago, when I snatched another chance to get the observatory roof open and do a bit more astrophotography.

Target Acquired...

It had been quite a while since I last tried to image M51, AKA The Whirlpool Galaxy.  In fact, looking back through my archive, I see that it was circa August 2016 when I last collected the photons travelling from this popular target.  Back then, I was using a completely different set of equipment and techniques.  I was using a DSLR and Backyard EOS to capture my data.  The mount I used back then was a Celestron AVX mount set up in the back garden of our old house.  Processing was carried out predominantly in Deep Sky Stacker and GIMP.
I've come on a bit since then, and now use an astro dedicated OSC camera on a Skywatcher EQ6-R Pro mount permanently set up in the observatory.  All the data is captured with SharpCap Pro and processed in PixInsight.
That's enough of the tech jargon, let's move on.

Data Acquired and Processed...

Originally, I wanted to collect between 3 and 3.5 hours of light data of M51, and then all the relevant dark and flat calibration frames on top of that.  In fact, that is precisely what I did, but I did seem to hit a big issue.  As part of the processing, I look at each individual frame to see if there are any anomalies which could affect the final results.  I found loads.  Out of approximately 36 frames, 8 of them had satellite trails going through them, so I removed them from the stack.  Only after I finished this image did I learn that there are techniques within PixInsight which can deal with satellite trails to some degree.  But that's a whole new topic for another day!
Onto the stacking and calibration, where for some reason, PixInsight failed to calibrate another bunch of the remaining frames.  I tried several different ways using different settings, but not making much difference.  In the end, I had to call it quits, and just run with the frames I could use.  I was now down to a total of 11 light frames, roughly 1/3 of the total I was originally hoping for.  Things weren't looking good and to be honest, I wasn't expecting much at all.  I was staring a completely wasted night in the face.

Victory Snatched...

Even though I didn't expect much from this set of data, I wanted to persevere through to the end result.  After all, you don't learn anything by giving up half way through if something doesn't work out.  Somehow, and I'm not sure how, I managed to salvage a very reasonable picture (in my opinion anyway) of M51, and when compared to my attempt from 4 years ago, I'm particularly heartened to see how far I have come.  So, without further delay, my most recent effort on M51 - The Whirlpool Galaxy.

M51 - The Whirlpool Galaxy.  11 x 5 minute light frames + approximately 25 flat frames and 30 dark frames for calibration.
Just to compare the difference, here's my attempt from back in August 2016.  It's a significant difference.

For comparison, my first attempt at M51 from August 2016
Time to wrap this post up.  Still to come over the next few days, I will look at the results of another couple of imaging sessions (although I haven't processed the data from those yet), a tour of the home observatory and the traditional blog post for Astrocamp, with a difference.
All the very best.  Stay safe!

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