Sh2-115

HOME
Sh2-115 Sh2-115
Emission Nebula in Cygnus

Click here for higher-resolution versions: 100% (4096x4096) 65% (2662x2662) 40% (1638x1638)

Click on image to toggle through the four versions (as explained below)

Sh2-115 is part of very large, quite faint (almost nothing of the nebula is visible on a single 15-minute exposure through the clear filter) molecular cloud, which includes Sh2-112 and Sh2-116. My image of Sh2-116 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). Sh2-115 is illuminated by the ionizing effects of the bright star cluster, Berkeley 90, below and to the left of the center of this image.

This area is about 7500 light years from us; at that distance, this frame is about 100 light years across.

I have presented this object in four 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), 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 is my favorite version, so it is on top of the stack; I like the vibrant colors and detail shown.

(ii) A true-color version (the second photo in the stack), 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 visual impact in the previous image compared to this image.

(iii) A version (the third photo in the stack) in the Hubble palette (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 green from the Ha emissions turned brownish, and de-emphasized in this rendition because they would be so dominant otherwise). I like the clear blue when a nebula has significant oxygen emissions, as is the case here. This form of combining results in magenta-colored stars, which I have significantly desaturated.

(iv) A pure-Ha version. I like the ghostly appearance and the contrasty look.

Technical Information:

Ha:OIII:SII:L:R:G:B: 750:600:600:555:180:180:260 (a total of a bit over 52 hours of light-frame exposure time); here's a chart showing the various subexposures I used in the image:

Hydrogen Alpha: 25 thirty-minute
Oxygen III: 20 thirty-minute
Sulfur II: 20 thirty-minute
Luminance: 33 fifteen-minute, and 20 three-minute
Red: 12 fifteen-minute
Green: 12 fifteen-minute
Blue: 13 twenty-minute
The luminance layer of the top image is a mix of the luminance-filtered images and the Ha-filtered images; the red channel is a mix of the red-filtered images and the Ha-filtered images; the green channel is a mix of the green- filtered images and the OIII-filtered images; the blue channel is a mix of the blue-filtered images and the OIII-filtered images. The SHO image is created by using the SII master as the red channel, the Ha master as the green channel, and the OIII master as the blue channel; because Ha is so dominant in this nebula, I had to significantly squelch that channel to get the colorful SHO image (which uses the Ha master as the luminance layer).

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 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 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 July and August of 2025. Image posted December 5, 2025.

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

Seeing: Generally very good.
CCD Chip temperature: -25C