Observation by Kevin Gurney: Sh2-91

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Kevin Gurney


Kevin Gurney


2022 Aug 06 - 23:24


2022 Aug 17 - 10:37


Sharpless 91

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Field centre

RA: 19h35m
Dec: +30°09'
Position angle: -10°01'

Field size

2°31' × 1°26'

  • William Optics Star71
  • Fornax 102
  • ZWO ASI1600MM pro
  • Baader narrowband filters
  • Atik EFW2
  • SX Lodestar X2

27x300s Ha, 24x300s OIII over two nights (6/7 August)


Charente, France

Target name




About this image

This was the Deep-Sky object of interest for August. I'ts part of a larger supernova remnant and the challenge was to image the whole structure which is around 4deg across. I tried this with a Canon 200mm lens and the ZWOASI1600m camera but I didn't have filters for this rig and the results were disappointing... you really need narrowband I think.

So I focussed on the designated part (Sh2-91) with the WO71 refractor. This object is hard to image! Its much fainter than the more well know Veil nebula. Good images in Astrobin have upwards of 12 (often > 30) hours of data... I didnt have the patience for this :) so my 4 hours 15mins of data are all I have. Captued in Voyager, Processed in PI. Ha in Red, OIII in Blue/Green

The other problem is the 'noise' supplied by the density of stars surrounding it.  I used star masking and morphological reduction in PI, but these always lead (at least in my hands) to somewhat odd-looking stars. However, on balance I think this helps bring out the nebula...


The bright red stellar object in the field looks artefactual but it turns out to be Campbell's Hydrogen Star (HD184738, V1966 Cyg) which is also a small planetary nebula.

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