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Sh2-116
Sh2-116
Emission Nebula in Cygnus
Click here for uncropped versions: 100% uncropped (4046x4066) 65%
uncropped (2630x2643) 40% uncropped (1618x1626)
Click on image to cycle through the six versions of the image (described below)
Sharpless 116 is a small emission nebula (formerly believed to be a planetary nebula, but a more recent study documented low levels of OIII emissions, indicating it's
not a planetary nebula), part of the much larger emission nebula which includes Sh2-112 and
Sh2-115. My image of Sh2-115 overlaps this image; to see a rough mosaic, stitching the two images together, click
here; Sh2-112 is on the other side of Sh2-115 from Sh2-116, and a bit farther away (so no overlap allowing it to be stitched to
the others).
This area is about 7500 light years from us; at that distance, Sh2-116 is about six light years across.
Most of the emission nebulae that I image can be successfully processed in a number of ways, each of which is pretty and interesting. Because of the paucity of OIII and SII in this
entire region, none of the other ways I processed the data was interesting to me, so I did not post any. I did weave some of the OIII and SII data into the color layer of this image.
The processing of this data set was immensely complicated by my needing to send my camera/filter wheel/AO-X back to SBIG for repair before I had gathered enough data. This necessitated
taking another set of flats for the later images taken after the return of the camera assembly.
I have presented this object in six different formats; I like each one in its own way. This is the order in which they appear as you cycle through (by repeatedly clicking on the photo, waiting for
each to download; each is labeled in the lower left corner), starting with a reddish version:
(i) A true-color version (the top photo in the stack, labeled "LRGBNB"), with the color created by imaging through red, green and blue filters (with a significant amount
of Ha and OIII data blended into various channels, in varying percentages; Ha emissions are in the red spectrum, and OIII emissions are blue-green, so I have blended Ha into the luminance layer and
the red channel, and OIII into the green and blue channels).
(ii) A true-color version (the second photo in the stack, labeled "LRGB"), with the color created by imaging through red, green and blue filters only (no Ha or OIII data
included). It is interesting to see how much the addition of the Ha and OIII increases the detail, but it's also interesting to note the more vibrant colors--especially star colors--that often appear
in the RGB version (this is the reason for hybridizing (ii) and (iii)--getting some of the detail from (iii) while keeping the more vibrant colors).
(iii) A bi-color version (almost true-color version; the third photo in the stack, labeled "HOO"), in which "red" is ionized hydrogen emissions (Ha), and the green and blue
channels both are doubly-ionized oxygen emissions (OIII), which are blue-green in color. It's a fair substitute for having red, green and blue channels, but, because the green and blue channels are
the same, there is a lot of blue-green color in the stars (which I have moderated in processing). It's interesting to me how close this came to the much more complex (with much more data) true-color
version above, but with some less color breadth; people who image from badly light-polluted locations often use this method, since narrow-band light is much less affected by the light pollution.
(iv) A version in the Hubble palette (the fourth photo in the stack, labeled "SHO"; lot of the Hubble photos, including and especially the famous "Pillars of Creation,"
are made with this set of filters, since it's a useful set for scientists to see what's actually happening), which shows SII emissions as red, Ha emissions as green, and OIII emissions as blue.
Because Ha emissions so dominate this nebula, I have significantly de-emphasized them in this rendering. With that, the OIII emissions show as pure blue (would be a blue-green otherwise), and
the SII emissions show as a ruddy brown/yellow (would really show up much otherwise). This form of combining results in magenta-colored stars, which I have significantly desaturated.
(v) A version in the Hubble palette (the fifith photo in the stack, labeled "SHOtan"; this is the same as the previous photo in the stack, except the greenish places
have been converted into tan.
(vi) A pure Ha version (the sixth photo in the stack, labeled "HA"), showing only emissions from the ionized hydrogen atoms in the nebula.
Technical Information:
(HaL)(HaSIIR)(OIIIG)(OIIIB): Ha:OIII:SII:L:R:G:B--660:720:630:555:120:135:280 (a total of almost 52 hours of exposures); luminance layer consists of blend of 33
fifteen-minute images using a luminance filter, 20 three-minute images using a luminance filter, and 22 thirty-minute images using an Ha filter; R channel is a blend of 8 fifteen-minute
images through a red filter, the Ha data also used in the luminance layer, and 21 thirty-minute images taken through an SII filter; G consists of 9 fifteen-minute images taken through a
green filter blended with 24 thirty-minute images taken through an OIII filter, while B is the combination of 14 twenty-minute images taken through a blue filter blended with the OIII
data.
Equipment: RC Optical Systems 14.5 inch Ritchey-Chrétien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an
SBIG STX-16803 with internal filter wheel (SBIG filter set), guided by an SBIG AO-X/STX Guider, all riding on a Bisque Paramount ME German Equatorial Mount.
Image Acquisition/Camera Control: Maxim DL, controlled with ACP Expert/Scheduler, working in concert with TheSky X.
Processing: All images calibrated (darks, bias and sky flats), aligned, and combined (using NormalizeScaleGradient) in Pixinsight. Color combine in Pixinsight.
Narrow-band data blended into the luminance and color layers in Pixinsight. Some finish work (GradientCorrection, background neutralization, color calibration, NoiseXTerminator,
BlurXTerminator, done in Pixinsight; some finish work (LRGB combination, saturation adjustment) was done in Photoshop CC.
Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.
Date: Images taken on many nights during June, July, August, October and November of 2024. Image posted February 10, 2025.
Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.
Seeing: Variable, with individual calibrated luminance images having FWHM varying from 1.9 to 3.2 arcseconds.
CCD Chip temperature: -25C
Copyright 2024, 2025 Mark de Regt
