Hemisphere:  Southern  ·  Contains:  B85  ·  M 20  ·  M20  ·  NGC 6514  ·  Sh2-30  ·  Trifid Nebula  ·  Trifid nebula
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M20, Trifid Nebula, LSHO, 27-29 May 2020, 


            David Dearden
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M20, Trifid Nebula, LSHO, 27-29 May 2020

Imaging telescopes or lenses: Astro-Tech AT8IN

Imaging cameras: ZWO ASI1600MM-Cool

Mounts: Skywatcher NEQ-6 Pro Synscan

Guiding telescopes or lenses: Astro-Tech AT8IN

Guiding cameras: ZWO AS120MM-Mini

Focal reducers: High Point Scientific Coma Corrector Photo & Visual For Netwonian Telescopes 2"

Software: DeepSkyStacker  ·  Noel Carboni's Astro Tools for PhotoShop  ·  StarTools  ·  AstroPlanner  ·  PHD2 Guiding  ·  Sequence Generator Pro  ·  EQASCOM  ·  photoshop  ·  Enterprise Astronomy Annie's Astro Actions

Filters: ZWO SII 7nm  ·  ZWO Luminance 31 mm  ·  ZWO OIII 31 mm 7 nm  ·  ZWO H-alpha 7nm

Accessory: Orion Thin Off Axis Guider (TOAG)  ·  Robert Brown's Arduino ASCOM Focuser Pro DIY  ·  ZWO EFW filter wheel

Dates:May 27, 2020May 28, 2020May 29, 2020

ZWO H-alpha 7nm: 22x300" (gain: 139.00) -20C bin 1x1
ZWO Luminance 31 mm: 49x180" (gain: 139.00) -20C bin 1x1
ZWO OIII 31 mm 7 nm: 22x300" (gain: 139.00) -20C bin 1x1
ZWO SII 7nm: 24x300" (gain: 139.00) -20C bin 1x1

Integration: 8.1 hours

Avg. Moon age: 5.67 days

Avg. Moon phase: 32.50%

Bortle Dark-Sky Scale: 5.00

Astrometry.net job: 3569251

RA center: 18h 2' 36"

DEC center: -22° 57' 51"

Pixel scale: 1.720 arcsec/pixel

Orientation: 2.021 degrees

Field radius: 0.696 degrees

Resolution: 2308x1780

Locations: Mapleton Lateral Observatory, Mapleton, Utah, United States

Data source: Backyard


4100 ± 200 ly

I have not been particularly happy with my prior images of M20. It’s difficult to image from my location because it is low on my southern horizon (transit altitude 27°) so I don’t get a lot of good imaging time, but fortunately this is a fairly bright target so I can get away with a bit less time. Of course this is one of the iconic astrophotography targets so I very much want to get a decent image. For this attempt, I collected data over several nights while dodging cloudy weather. I wanted to get HSOLRGB, and I still don’t have the RGB, but have enough to put the narrowband data together. I’m glad to have L. I don’t think I could use Hα for L because Hα doesn’t pick up the blue reflection part of the nebula. OIII gets some of that but shows less detail in the emission part. So L is important here. The two renditions here are LSHO as provided by Annie’s Astro Actions and LHSO as built by me. As usually seems the case, the Hubble palette seems to bring out more detail. I’m looking forward to seeing how RGB looks; I suspect the dust will show up better with the B filter, and I like RGB stars. I tried composing everything in StarTools from linear data, but that did not work as well as processing and optimizing each of the channels separately and then combining the color layers in Photoshop.

Date: 27-29 May 2020
Subject: M20, Trifid Nebula
Scope: AT8IN+High Point Scientific Coma Corrector
Filters: ZWO 31 mm diameter unmounted L, Hα, OIII, SII
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + ASI120MM-mini +PHD 2.6.8 (Win 10 ASCOM)
Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21
Acquisition: Sequence Generator Pro
Exposure: 49x180 L, 22x300 Hα, 22x300 OIII, 24x300 SII
Stacking: Deep Sky Stacker 4.2.3 (64-bit) dark+flat+bias, κ-σ stacking with κ = 1.5
Processing: StarTools 1.6.394RC: Separately optimized L, Hα, OIII, and SII, using pretty much the same procedure for each. Software binned 2x2, cropped, developed (~92%), HDR (reveal all), deconvoluted slightly (2 pixels), and untrack denoised. In Photoshop, combined layers with Annie’s Astro Actions, then applied the L. Some levels adjustments. AstroFrame.



David Dearden
License: None (All rights reserved)


  • Final
    M20, Trifid Nebula, LSHO, 27-29 May 2020, 


            David Dearden
  • M20, Trifid Nebula, LSHO, 27-29 May 2020, 


            David Dearden


Description: Same data, but combined LHSO for a more “natural” look.

Sky plot

Sky plot


M20, Trifid Nebula, LSHO, 27-29 May 2020, 


            David Dearden