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Sh2-155 The Cave Nebula in Narrow Band

Technical card

Resolution: 3117x3117

Dates:Sept. 6, 2019Sept. 11, 2019Oct. 15, 2019

Astrodon Ha, 5nm: 48x1200" -25C bin 1x1
Astrodon OIII, 5nm: 64x1200" -25C bin 1x1
Astrodon SII, 5nm: 43x1200" -25C bin 1x1

Integration: 51.7 hours

Darks: ~17

Flats: ~17

Bias: ~19

Avg. Moon age: 12.11 days

Avg. Moon phase: 81.63%

Mean SQM: 21.35

Mean FWHM: 2.10

Temperature: 4.33 job: 3091152

RA center: 344.327 degrees

DEC center: 62.595 degrees

Pixel scale: 0.478 arcsec/pixel

Orientation: 90.134 degrees

Field radius: 0.293 degrees

Locations: Deep Sky West, Rowe, NM, United States

Data source: Own remote observatory

Remote source: DeepSkyWest


Sh2-155 was first named "the Cave Nebula" by Patric Moore. It is a relatively large region in the sky that's full of both emission and dark nebula located in the constellation of Cepheus at a distance of about 2,400 ly. Even though the visual magnitude is listed at 7.7, this is a very challenging narrow band object due to the very low brightness of both SII and OIII emissions. It requires a pretty serious commitment in exposure time to successfully image this object in narrowband, which I suspect is why most images are taken in LRGB.

I started on this project after shooting galaxies when the moon was waxing and I needed a new narrowband project. My feeling at first was, "How hard can it be?" and I learned first hand. This is definitely a hard one! I started in early September and took my last data set in late November. Along the way, I took a 3-week trip to New Zealand so I got to experience running my scope from the other side of the planet. The problem was that I had to start the scope at about 3 pm NZ time, which was tough because I was usually out having fun until early evening. So, I lost a lot of available sky time. Fortunately my scope performed reasonably well during this whole period with only a few unexpected hang ups. The spectacular October weather in New Mexico slowly deteriorated so I had to relax my standards a bit to keep roughly half of the data that I gathered.

In spite of over 50 hours of data, this was still a challenging processing project. The signals are very weak, which always increases the difficulty of noise mitigation. Furthermore, the cave doesn't include much of the kind of fascinating detail that I like to see in emission nebula. There's some but with the low SNR, it's hard to emphasize it. Still, it's an interesting NB object.

As always, I'm happy to hear your C&C so feel free to let me know what you think.

- John



John Hayes
License: None (All rights reserved)


Sky plot

Sky plot


Sh2-155 The Cave Nebula in Narrow Band, 


            John Hayes

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