Iris Nebula - Caldwell 4, NGC 7023, LBN 487 (RGB8), 



Iris Nebula - Caldwell 4, NGC 7023, LBN 487 (RGB8)

Iris Nebula - Caldwell 4, NGC 7023, LBN 487 (RGB8), 



Iris Nebula - Caldwell 4, NGC 7023, LBN 487 (RGB8)

Acquisition details

April 19, 2021
ZWO UV-IR: 169×60(2h 49′) (gain: 0.00) -10°C
2h 49′
Avg. Moon age:
6.65 days
Avg. Moon phase:
Bortle Dark-Sky Scale:

Resolution: 2939x2942

File size: 12.1 MB

Locations: Backyard, Roebling, New Jersey, United States

Data source: Backyard


Sometimes called the Iris Nebula, NGC 7023 is about 6 light-years across, and 1,300 light-years away in a dusty part of the Milky Way. Located in the constellation Cepheus, dusty nebular material surrounds a massive, hot, young star in its formative years. Central filaments of cosmic dust glow with a reddish photo-luminescence, as some dust grains effectively convert the star's invisible ultraviolet radiation to visible red light. Yet the dominant color of the nebula is blue, characteristic of dust grains reflecting starlight. Dark, obscuring clouds of dust and cold molecular gas are also present and can lead the eye to see other convoluted and fantastic shapes. Infrared observations indicate that this nebula may contain complex carbon molecules known as PAHs.

There is also an open cluster of stars associated with NGC 7023, known as Collinder 427. This loose open cluster can be seen here on the right side of the reflection nebula, within the dark region above the "petal" structure of the Iris.


-William Optics Zenithstar 73mm FPL-53 doublet APO refractor.

-William Optics Flat73r focal reducer/field flattener.

-SkyWatcher EQ6R-Pro equatorial mount.

-ZWO ASI533MC-Pro color camera with ZWO luminance filter.

-William Optics Uniguide 32mm guide scope.

-ZWO ASI462MC color camera with Antlia 685nm IR-pass filter.

-ZWO ASIair Pro.

Pre-processing/Calibration performed in DeepSkyStacker:

-169 60-second lights (gain 0), calibrated with temperature matched darks, flats, and bias frames (30 each at minus 10 degrees Celsius).

-Debayered with Auto Homogeneity Directed interpolation.

-Stacked with Auto Adaptive Weighted Average algorithm.

-Export to 3-plane FITS.

Post-processing performed in Siril:


-Background Extraction.

-Photometric Color Calibration.

-Arcsinh Transformation.

-Histogram transformation.

-Color Saturation.

-Export to TIFF.

Final image adjustments performed in GIMP:

-Fine tune black level (Levels).

-Fine tune colors (Curves).

-Export to PNG.

Shot from my light polluted back yard (Bortle 6-7) under a 48% illuminated waxing half Moon.



Iris Nebula - Caldwell 4, NGC 7023, LBN 487 (RGB8),