Imaging Diary - M81 & M82

Essential Information

• Name M81 Bode's Galaxy and M82 The Cigar Galaxy
• Constellation Ursa Major
• RA 09h55m33s (M81) & 09h55m52s (M82)
• DEC +69°03′55″ (M81) & +69°40′47″ (M82)
• Apparent Magnitude 6.94 (M81) & 8.41 (M82)
• Apparent Size 26.7′ x 14.1′ (M81) & 11.2′ x 4.3′ (M82)
• Actual Size 90,000ly (M81) & 37,000ly (M82)
• Distance ~12 million light years from Earth for both objects

An "Easy" Target

I've seen countless variations of this pair of galaxies owing to their excellent characteristics and relative ease of capturing for someone in the Northern hemisphere:

• They're big - Galaxies are small targets that like long focal lengths but M81 by itself is one of the largest galaxy targets from Earth, coupled with smaller M82 very close by (in terms of observation - cosmically speaking they are ~300,000 ± 200,000 light years from one another)
• They're bright - At 6.94 & 8.41 magnitude respectively they are relatively bright compared to some other galaxies
• They're high - In Ursa Major (or the Plough/Big Dipper if you prefer) they remain circumpolar in most of the Northern hemisphere, so they remain relatively close to the pole and during Spring 'galaxy season' they are up near the Zenith where there is very little of the Earth's atmosphere getting in the way.

First Of Many

This was my first Galaxy target and first serious imaging session of 2020 and also the first after getting my custom DIY OnStep EQ5 fully functional and in a spot where it was working well. It also marked the arrival of my new ZWO ASI290MM Mini guide/planetary camera which replaced a Datyson T7C clone of the ZWO ASI120MC Mini which developed problems with its USB connection after only a few months of actual usage mainly for testing purposes.

Before this I had captured M42 Orion Nebula in late January but it was getting ever lower in the sky as the days wore on as it moves back below the horizon for spring and summer imaging season along with the other nearby winter targets. Having only achieved 1.2 hours on M42 this was my first "true" image with multiple hours of exposure, essential for improving that vital Signa-to-Noise (SNR) ratio so important in astrophotography.

Moving Forwards

This was a truly stunning result for me and a real sense of achievement after putting in so many hours of work since the Autumn in 2019 when I first got the OnStep EQ5 up and running.

What followed were several nights of "tweak then test" with the sparse amount of clear nights available over what was agreed on some UK astronomy forums one of the worst winter seasons for astronomy ever with only a handful of cloudless nights over nearly all of October-December 2019.

With this image of M81 & M82 however it marked a turning point in my journey and from here I've had session after session of successes which I look forward to sharing with you on this site over several more of these "Imaging Diary" posts!

Acquisition Details

• Date - 2020-03-22
• Imaging Scope - Skywatcher 130PDS @ 650mm
• Imaging Camera - Canon 400D Astro-Modified for Ha response
• Guide Scope - Svbony 50mm Guide Scope
• Guide Camera - ZWO ASI290MM Mini
• Light Frames - 38x300s for 3.2 hours total
• Dark Frames - 10x300s
• Flat Frames - 50x0.5s with DIY Flat Planel
• Flat-Dark Frames - 50x0.5s
• Bias Frames - 50x0.00025s (1/4000 minimum exposure on camera)
• Moon Age - 28 days
• Moon Phase - 3.2%
• Bortle Sky - Class 5 Suburban Skies
• Pixel Scale - 1.8 arcseconds per pixel
• Field Radius - 1.085 degrees
• Platsolving - Astrometry.net Solution
• Astrobin - Astrobin Link

Processing Details

• Stacking - Astro Pixel Processor

  • Calibrated Light frames with Bias/Flat/Dark/Dark Flat
  • Registered and performed Local Normalisation without Background Neutralisation
  • Integrated best 85% of frames for 38 total
  • Drizzled with Bayer Drizzle at Scale 2.0 and TopHat Kernel at 1.0 droplet size
  • Saved final stacked image in linear 16bit FITS format

• Processing - StarTools

  • Bin - Image 50% back to original size
  • AutoStretch - Reveal image and problems
  • Crop - Removed edges of stack and worst coma
  • Wipe - Remove light pollution gradients
  • AutoDev - Re-do Stretch with Trunk as Region of Interest (ROI)
  • Contrast - Push background down and bring signal forwards
  • HDR - Reveal large scale structures
  • Sharp - On 'Large' to reveal medium-Large scale structure detail
  • Decon - Reverse atmospheric seeing effects and reveal medium-scale detail
  • Life - 'Less=More' preset to reduce background, enhance nebulosity
  • Color - bring colours as close to natural as possible
  • Tracking Off - Grain Equalisation noise reduction at large scale to remove worst noise
  • Flux - Introduce small amount of sharpening back into the image on areas exclusding stars
  • Shrink - Reduce star sizes by 1 pixel

• Final Touches - Photoshop CC 2020

  • Duplicate - Original image to save original state in bottom layer
  • HLVG - Hasta La Vista Green to remove residual green cast from the image
  • Duplicate - Copy the HLVG applied image for fallback purposes
  • Camera RAW Filter - Apply balancing to White, Black, Shadows, Highlights, Saturation to balance overall image
  • Camera RAW Filter cont. - Apply small amount of sharpening, smooth noise with Luminosity Noise Reduction, Colour Noise Reduction
  • Curves Adjustment Layer - Apply curves layer on top of the image to introduce a subtle s-curve to bring up highs, bring down lows for overall final contrast tweaks