Hemisphere:  Northern  ·  Contains:  Crescent nebula  ·  NGC 6888
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Crescent Nebula in Synthetic RGB, 


            Frank Kane
Crescent Nebula in Synthetic RGB
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Crescent Nebula in Synthetic RGB

Technical card

Imaging telescopes or lenses: Sky-Watcher StarLux 190MN

Imaging cameras: Atik 383L+

Software: Software Bisque The Sky X Pro  ·  Adobe Phosotshop CS6  ·  Pleiades Astrophoto PixInsight

Filters: Astronomik 6nm H-alpha OII and SII

Accessory: MoonLite Focuser w/High Res Stepper Motor

Dates:May 25, 2019

Frames: 48x240"

Integration: 3.2 hours

Avg. Moon age: 21.09 days

Avg. Moon phase: 61.16%

Basic astrometry details

Astrometry.net job: 2709501

RA center: 20h 12' 26"

DEC center: +38° 13' 37"

Pixel scale: 1.113 arcsec/pixel

Orientation: 85.415 degrees

Field radius: 0.443 degrees

Resolution: 2364x1617

Locations: Merritt Island home, Merritt Island, FL, United States

Data source: Backyard


The Crescent Nebula (NGC 6888) imaged with narrowband filters from a suburban driveway, converted to RGB using an algorithm that tries to recreate its natural appearance from narrowband data. It's a way to beat light pollution while still getting fairly natural-looking colors. The details are at http://boldly-going.com/2019/05/21/beating-light-pollution-with-a-new-synthetic-rgb-algorithm/ and you'll also find the larger image this was cropped from there.

For this image I derived a slightly different RGB mapping that takes into account the fact that my filters are narrow enough to exclude the second O3 emission line, and synthesizes it as well:

R = 0.5*Ha + 0.5*SII
G = 0.695*OIII + 0.094*Ha
B = 0.411*OIII + 0.1*Ha

It didn't make much of a visual difference, but in theory it's a little bit closer to reality.

Other processing notes:
- I love Mure Denoise
- OIII and SII data wasn't awesome, so I used Hydrogen-alpha as a luminance channel. Unfortunately this means a faint shell of OIII ahead of the nebula got lost, but the image is significantly sharper as a result.
- I de-saturated everything a little outside of the Crescent itself, to make the stars a little less distracting in the image.



Frank Kane
License: None (All rights reserved)

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Crescent Nebula in Synthetic RGB, 


            Frank Kane