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Contains:  NGC 7822
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Sh2-171, SHO Hubble Palette with RGB Stars, September 2018, 


            David Dearden
Sh2-171, SHO Hubble Palette with RGB Stars, September 2018

Sh2-171, SHO Hubble Palette with RGB Stars, September 2018

Technical card

Resolution: 2253x1655

Dates:Sept. 8, 2018Sept. 10, 2018Sept. 11, 2018

ZWO Blue 31 mm: 20x180" (gain: 139.00) -20C bin 1x1
ZWO Green 31 mm: 16x180" (gain: 139.00) -20C bin 1x1
ZWO H-alpha 7nm: 21x600" (gain: 139.00) -20C bin 1x1
ZWO OIII 31 mm 7 nm: 24x600" (gain: 139.00) -20C bin 1x1
ZWO Red 31 mm: 20x180" (gain: 139.00) -20C bin 1x1
ZWO SII 7nm: 23x600" (gain: 139.00) -20C bin 1x1

Integration: 14.1 hours

Avg. Moon age: 10.31 days

Avg. Moon phase: 2.46%

Bortle Dark-Sky Scale: 5.00 job: 2253312

RA center: 0.892 degrees

DEC center: 67.214 degrees

Pixel scale: 1.719 arcsec/pixel

Orientation: 4.641 degrees

Field radius: 0.667 degrees

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

Data source: Backyard


I had thought this was a first-attempt image of Sh2-171, but looking through my older files I see I did it 2 years ago in Hα, one of the last images I took with the DSI IIc acting as my main imager (before I upgraded to the ASI1600MM-Cool). At any rate, the current image took advantage of several consecutive nights of good skies just before the mountains southwest of me caught fire (with pretty good wind out of the southwest = heavy smoke), ruining any imaging opportunities for now. Sh2-171 is relatively bright in Hα, not so much in OIII, but shows interesting detail in SII that adds a lot to the image. I don’t usually do 600 sec subframes but this target seemed to need them. To top it off, I took some shorter-exposure RGB intending to just use that for the stars (and that’s exactly how I used it in this image), but then I realized we have just looked at the H atomic spectrum in my freshman chemistry class as build up toward the quantum mechanical atom. I pointed out the Hα line then, and intend to show several versions of this image (Hα only, RGB only, and Hubble Palette) in my next lecture to illustrate how much information you can get using narrowband imaging. Spectroscopy lets you know the chemistry of distant objects. So I’m having some fun with this.

Date: 8-11 Sep 2018
Subject: Sh2-171
Scope: AT8IN+High Point Scientific Coma Corrector
Filters: ZWO 31 mm diameter unmounted 7 nm Hα, SII, OIII, R, G, B
Mount: EQ-6 (EQMOD 2.000j)+PEC
Guiding: Orion Thin Off-axis Guider + DSI IIc +PHD 2.6.5 (Win 10 ASCOM)
Camera: ASI1600MM-Cool, -20 °C, Gain 139 Offset 21
Acquisition: Sequence Generator Pro
Exposure: 21x600 Hα, 23x600 SII, 24x600 OIII, 20x180 R, 16x180 G, & 20x180 B
Stacking: Deep Sky Stacker 4.1.1 (64-bit) dark+flat (no bias), κ-σ stacking with κ = 1.5.
Processing: StarTools 1.4.332: Cropped Hα but did not wipe, then stretched, applied HDR (optimize), masked out the “fat” stars, aggressively deconvoluted, then did untrack denoise. Followed essentially the same procedure for SII and OIII. Combined SHO in Photoshop using Annie’s Astro Actions, and played with the color balance to get it roughly how I thought it should look. Did several rounds of curves + levels and some Carboni deep space noise reduction. Combined R, G, & B in StarTools. Cropped but no wipe was needed, developed, HDR optimized, and applied default color module settings. Denoised without any deconvolution. Added the RGB stars on top via screen combine. Used a couple of rounds of “increase star color”, followed by a couple of rounds of “make stars smaller”. AstroFrame.



David Dearden
License: None (All rights reserved)


  • Final
    Sh2-171, SHO Hubble Palette with RGB Stars, September 2018, 


            David Dearden
  • Sh2-171, SHO Hubble Palette with RGB Stars, September 2018, 


            David Dearden


HSO from the same data. It's interesting that the SHO shows the contrast better, which is I suppose why the Hubble Palette is so useful.

Sky plot

Sky plot


Sh2-171, SHO Hubble Palette with RGB Stars, September 2018, 


            David Dearden