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Observation by Ron Morley: M101 Pinwheel Galaxy

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Ron Morley


Ron Morley


2020 Apr 14 - 22:30


2020 Apr 21 - 14:22


The Triangulum Galaxy (M33)
The Coma Pinwheel Galaxy (M99)

  • Takahashi 60mm refractor FS60C
  • SX Ultrastar Mono camera
  • Baader RGB absorptive filters with UV/IR block
  • Piggy-backed on Meade LX200 10"
  • Exposures taken using Starlight Live. Pre and post processing using Astroart 7

Two sets of 5 minute exposures for Luminance and RGB plus corresponding flats and darks


Perth and Kinross

Target name

Pinwheel Galaxy M101


M101 Pinwheel Galaxy

About this image

This was my first attempt at RGB imaging.  The exposures were unguided. Considerable time had been spent over the preceding weeks in refining the polar alignment (PTFE washers on wedge and SharpCap 3.3 method), worm training and tube balancing.  Flats were taken using 315mm Aurora flatfield panel mounted on an extendable (3m high) camera tripod. Panel held in position using an articulated iPad clamp.  A layer of thin card was inserted to reduce the luminosity of the panel.   M101 was around altitude 75 degrees. Minor unsharp mask applied to luminance.  Combined LRGB colour image used unadjusted Astroart settings.  The Takahashi optics are excellent, the Ultrastar is a very good high-end guide camera but the Meade wedge/tracking system is modest.  Satellite trails caused 30% of images to be discarded which suggests 5 minutes is about the longest you can economically manage these days.

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John Hughes
John Hughes, 2020 Apr 21 - 15:09 UTC

 Thats a great first image Ron and impressive at 5 minutes unguided. All that prep work before hand certainly played its part.

 Thank you for sharing your image here.


Paul Leyland
Paul Leyland, 2020 Apr 21 - 19:03 UTC

In my experience, median stacking allows frames with minor pollution from satellites and cosmic ray hits to be used without serious effects on either aesthetics or scientific value.

Did you use median stacking or something else, such as average stacking?

Sigma clipping can also work well, I'm told,but median stacking is what I use.

Ron Morley
Ron Morley, 2020 Apr 22 - 13:38 UTC

Hi John,  Thank you for your kind words.  Imaging can be a bit of a slog so your encouragement is appreciated. Ron

Ron Morley
Ron Morley, 2020 Apr 22 - 13:46 UTC

Hi Paul,  Thank you for your helpful comments.  I used 'average' stacking for the image.  I carried out a rapid re-processing today using 'median'.  It did help.  One of the thick satellite streaks unfortunately went right across the centre of M101 but the fainter ones further away from the object could be dimmed to acceptable levels.  Thank you for your kind advice.  Ron

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