Caldwell 66 (NGC5694) - Globular Cluster in Hydra (James Tickner)

Caldwell 66 (NGC5694) - Globular Cluster in Hydra

Continuing to work through the list of Caldwell globular clusters, C66 is something of an oddity. At 10th magnitude and only about 3-4' across, it appears relatively small and insignificant. This is due to its great distance, about 114 kly from earth and about 96 kly from the galactic centre. Given that the diameter of the Milky Way is itself only about 100,000 light years, this means C66 lies well outside the galactic rim. There is some suggestion that this may be an intergalactic object captured at some point by our galaxy.

As far as I can tell this is only the second time that C66 has been imaged on Astrobin, with @Gary Imm grabbing the first shot!

Original
Final
B

B

Description: Although nice bright targets that respond well to fairly short integration times, globular clusters do present some challenges, particularly with sharpness, star shape and natural-looking colours. Using just the basic free processing tools such as GIMP makes achieving consistent results rather difficult.
To counter this, i've tried to develop some pre-processing tools that take out some of the guesswork, based on mathematical descriptions of different approaches I've found on the web.
The basic workflow now consists of:
- Stacking using DSS
- Simple black point adjustment based on identifying the global pedestal levels in R, G and B
- Global white-balance based on average RGB values for stars
- Colour preserving arcsinh stretch
- Non-uniform background correction based on measuring the RGB pedestals on a 20x20 grid covering the image and subtracting a smoothed surface passing through these values
- Final touchup in GIMP (denoising, sharpening, tweaking the stretch)
Overall the approach seems to preserve star colours better and give a more 'natural' look (at least to my eyes). Feedback welcome!

Uploaded: ...

Caldwell Globular Clusters

	Distinct awarded users	Total awarded images
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	Image of the day	Top pick	Top pick nominations	Total submitted
Deep sky
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Extremely wide field
Star trails
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Noctilucent clouds
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	Image of the day	Top pick	Top pick nominations	Total submitted
Backyard
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Own remote observatory
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Mix of multiple sources
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Unknown

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Status	Advanced success
Started	...
Astrometry.net job	6279681
PixInsight job	C4VAOGD8TWMYCX2WGCP30OWSRDPEG7EA
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	14h39m36s.767
RA (top/left)	14h41m12s.394
RA (top/right)	14h38m48s.961
RA (bottom/right)	14h38m01s.330
RA (bottom/left)	14h40m25s.650

Dec (center)	-26°31′22″.78
Dec (top/left)	-26°28′23″.100
Dec (top/right)	-26°12′38″.85
Dec (bottom/right)	-26°34′16″.97
Dec (bottom/left)	-26°50′04″.69

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