A Blue Spiral in Draco the Dragon

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Caldwell 3

I stumbled upon Caldwell 3, also known as NGC 4236, while looking through deep sky surveys to find a unique target to image.

This blue spiral galaxy is rarely imaged by amateur astrophotographers. It has a very low surface brightness and requires hours of imaging time before the faint arms can become visible.

Caldwell 3 is part of the M81 Galaxy Group, residing about 12 million light years away.

Some very faint integrated flux nebulae (IFN) started to become visible, causing the cloudiness appearing on the left half of the image and around certain bright stars.

The faint galaxies which pepper the background have even less information available about them; many simply a name and some basic photometry data. Many of the small ones are located hundreds of millions of light years away.

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Constellation: Draco

Coordinates: RA: 12h 09m 30s Dec: +69 23’ 52”

Dates Acquired: Feb. 19-20 & Feb. 24 2024

Moon Illumination (average): 86%

Bortle Class: 6

Latitude: +43°

Equipment Info:

Telescope: William Optics Grand Tourismo 71 with 6AIII Flattener/Reducer

Focal Length: 335.2mm

f/4.2

Main Camera: ZWO 533MM-Pro

Guide Camera: ZWO 290MM-mini

Mount: Sky Watcher EQ6Ri-Pro

Filters: Astrodon 31mm (LRGB)

Integration:

Lum: 234 x 120s

Red: 61x 120s

Green: 67 x 120s

Blue: 65 x 120s

Calibrated with flats & dark flats

Total Integration: 14h 14m

Processing Techniques - PixInsight Workflow:

1. WBPP & GraXpert - LRGB

2. RGB - RGBCombination, SPCC

3. L - BlurXTerminator

4. GeneralizedHyperbolicStretch on L and RBG

5. StarXTerminator on L & RGB

   • LocalHistogramEqualization with RangeSelection & GAME script masking on L-Starless

   • SCNR-Green , CorrectMagentaStars, Curves on RGB-Stars

   • Curves on RGB-Starless

   • PixelMath to recombine stars & starless:

     RGBK = combine(stars, starless, op_screen())

6. Apply L to RGB via LRBGCombination

7. Crurves on LRGB