Sh2-112

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Sh2-112 Sh2-112
Sharpless 112
Emission Nebula in Cygnus

Click here for higher-resolution versions: 40% (1598x1606) 65% (2597x2610) 100% (3996x4016)

Click on image to cycle through the six versions of the image (described below and labeled on the lower left corner of each image)

Sh2-112 is an emission nebula visually located in the summer constellation Cygnus (the heart of the Milky Way, which explains the dense starfield). It is predominantly red, because (i) ionized hydrogen emits in the red part of the spectrum; (ii) the vast majority of the light matter in the universe is hydrogen, and (iii) the hydrogen in this image is being ionized (stripped of its electron) by a highly-energetic young star inside the hydrogen cloud.

The nebula is thought to be about 5600 light years from Earth; at that distance, the brighter part of the nebula would be 37 light years across. Visually, it is about half the width of a full moon.

I have presented this object in six different formats (each image is labeled in the lower left corner); I very much 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):

(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); this method usually produces what is, to my eye, the most pleasing overall effect, with smaller stars, but still good colors;

(ii) A true-color version (the second photo in the stack, labeled "LRGB"), without using any narrow band data (all color is derived from data collected through red, green and blue filters), as a comparison to the result when loaded with NB data. I always like the rich colors (especially in the stars) that this method exhibits but the larger stars than the LRGBNB version, together with more of them, can overpower the nebula; );

(iii) A bi-color version (almost true-color version; the third photo in the stack, labeled "HOO"), in which "red" is a 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 (i) the red is a bit odd in color, and (ii) because the green and blue channels are the same, there is a lot of blue-green color);

(iv) A version in the Hubble palette (the fourth photo in the stack, labeled "SHO"; a 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 (with the Ha emissions de-emphasized in this rendition because they would be so dominant otherwise--but I still keep a lot of green in the nebula). I like the clear blue when a nebula has significant oxygen emissions.

(v) A version in the Hubble palette (the fifth photo in the stack, labeled "SHOtan") but converting the green to a tan/orange; this is popular, because the green can be overwheilming to the eye.

(vi) A pure Ha version (grayscale, showing only light in the very narrow Ha band); this is fun for me to gaze at in full resolution, to see all the detail. It's also what I use for the detail layer in the HOO and two SHO versions.

I gathered this data set in 2020 and 2021, and was pleased with the images I got then from of the data. But skills improve over time (hopefully), and tools certainly improve over time, so I sometimes reprocess old data. I reprocessed this data set in 2025, to produce the images posted here. If you want to see the earlier processing results, click here.

This object reminds me a lot of the Pacman Nebula.

Technical Information:

Ha:OIII:SII:L:R:G:B: 660:660:660:675:180:180:240 (a total of over 54 hours of light-frame exposure time); luminance, red and green exposures were all 15-minute exposures; blue all 20-minute exposures; Ha, SII and OIII were all 30-minute exposures.

Equipment: RC Optical Systems 14.5 inch Ritchey-Chretien carbon fiber truss telescope, with ion-milled optics and RCOS field flattener, at about f/9, and an SBIG STX-16803 camera with internal filter wheel (SBIG filter set), guided by an SBIG AO-X, 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, combined and cropped in Pixinsight. Color combine in Pixinsight. Some finish work (background neutralization, color calibration, NoiseXterminator and BlurXterminator) done in Pixinsight; some cleanup finish work was done in Photoshop CC.

Location: Data acquired remotely from Sierra Remote Observatories, Auberry, California, USA.

Date: Images taken on many nights in October, November and December of 2020, and August, September and October of 2021. Image posted November 5, 2021.

Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.

Seeing: Generally good, with individual calibrated luminance frames varying from 1.9 to 2.4 arcsecond FWHM.

CCD Chip temperature: -25C

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