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IC 1396A
IC 1396A
Elephant's Trunk Nebula
Emission Nebula in Cepheus
Click here for higher-resolution versions: 40% (1634x1634) 65%
(2656x2656) 100% (4086x4086)
Click on image to cycle through the five versions of the image (described below)
Sh2-86 is an emission nebula visually located in the constellation Cepheus. It is predominantly red in the true-color versions, because (i) ionized hydrogen emits in
the red part of the spectrum, and (ii) the hydrogen in this image is being ionized (stripped of its electron) by the highly-energetic young stars being formed in this hydrogen cloud. The pillar
dominating the middle of the image is a large column of gas and dust, in which star formation is taking place. The column was shaped, and is continually sculpted, by the action of the
energetic stars being formed in the cloud.
The bright colors in the top photo are a result of using the same "narrow band" filters (filters which allow only a narrow bandwith of light to pass) often used by Hubble and the JWST. This shows
emissions from ionized hydrogen, ionized sulfur and doubly-ionized oxygen. It is not "true color." Rather, it is used to highlight where certain emissions originate; using broad filters, as
are normally used, results in the predominately red image below the SHO image in the stack. I often process a version of a photo of an emission nebula to show the Hubble palette, but I usually
prefer a "true color" version to the Hubble palette version, aesthically. For this particular object, however, I like the Hubble palette version best, so I have placed it at the top of the stack.
The field is thought to be about 2400 light years from Earth; at that distance, the part of the "Elephant's Trunk" showing in this photo is about 23 light years long. Visually, it is a little less
than the width of a full moon in our sky.
I have presented this object in five different formats; I find each one interesting 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), starting with the bright blue and brown version (labeled "SRO" on the lower left):
(i) A version in the Hubble palette ("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). I like the clear blue when a nebula has significant oxygen emissions. This form of combining results in magenta-colored stars (magenta is the
opposite of green in the standard color palette, so reducing the amount of green increases the amount of magenta), which I have significantly desaturated.
(ii) A true-color version (the second photo in the stack, labeled LRGBNB), with the color created by imaging through red, green and blue filters (with a significant amount of Ha blended into
the red channel and OIII blended into the blue and green channels; 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);
(iii) A true-color version (the third photo in the stack, labeled LRGB), with the color created by imaging through red, green and blue filters (with no narrow-band data included); I
like the vibrant star colors in this version, but the number and size of the stars can be distraction;
(iv) An almost-true color version, created by using the Ha for the red channel and the OIII for both the green and blue channels. This is used by a lot of amateurs,
because it requires much less imaging time, and it comes fairly close to "true color." One characteristic of this method is blue-green stars.
(v) 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.
Technical Information:
Ha:OIII:SII:L:R:G:B: 600:630:630:600:195:180:260 (a total of over 51 hours of light-frame exposure time); luminance, red and green exposures were all 15-minute exposures (plus I took a series
of 3-minute luminance images); blue all 20-minute exposures; Ha, SII and OIII were all 30-minute exposures. The luminance layer is a blend of the 3-minutes images taken through the luminance filter, the 15-minute images
taken through the luminance filter, and the images taken through the Ha filter. The red channel is a blend of the red-filtered data and the Ha-filtered data. The green channel is a blend of the green-filtered data
and the OIII-filtered data. The blue channel is a blend of the blue-filtered data and the OIII-filtered 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 camera 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, 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 July and August of 2025. Image posted November 24, 2025.
Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.
Seeing: Generally good
CCD Chip temperature: -25C
Copyright 2025 Mark de Regt