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Observation by John Hughes: Messier 81 and Companions

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Paul Downing, FRAS


John Hughes


2020 Mar 12 - 23:00


2020 Apr 11 - 12:03



Planetarium overlay


Ursa Major

Field centre

RA: 09h57m
Dec: +69°12'
Position angle: -4°10'

Field size

1°40' × 1°15'

  • William Optics Z103 APO Refractor
  • ZWO ASI1600mm Pro Cool camera
  • William Optics 50mm Guidescope
  • ZWO ASI290mm mini Guide Camera

L 19 x 120s & 98 x 60s Bin 1x1 R 10 x 60s Bin 2x2 G 10 x 60s Bin 2x2 B 15 x 60s Bin 2x2 Ha 46 x 300s Bin 1x1


North Essex, UK

Target name

Messier 81


Messier 81 and Companions

About this image

John reports having some issues with artefacts and also as this was his first attempt at combining LHaRGB the calibration of the lights with flats, darks and dark flats was a challenge. Warren A. Keller, author of Inside PixInsight was very helpful in an earlier question John put out to the PixInsight for Beginners Group on FaceBook and cleared up his confusion over calibration.

Ron Brecher's presentation on The Astro Imaging Channel on YouTube helped with a dust mote that wasn’t entirely cleared by John's master flat (Pixel Math section “if the pixels are this, do this, or do nothing”). Using this method helped him to slightly raise the brightness of pixels in the offending area leaving the rest of the image untouched.

The artefact? Well, as hard as he tried he couldn’t remove a lightish smudge to the left of Messier 81, but checking on the Astrobin website revealed that it was actually galaxy PGC28757!

John reports that this was a very challenging project, using five filters and the additional complication of imaging across multiple nights, but was well worth the time put in.

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