Sh2-142 (Sharpless 142)
Open Star Cluster with Emission Nebula in Cepheus
Click here for higher-resolution versions: 40% (1590x1564) 65%
(2584x2542) 100% (3976x3911)
Click on image to cycle through the five versions of the image (described below and labeled on the lower left corner of each image)
NGC7380 is an open star cluster surrounded by a gas/dust cloud, in which star-forming is taking place. The emission nebula (included in the Sharpless catalog as Sh2-142)
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 near the new stars
is being ionized (stripped of its electron) by the highly-energetic young stars being formed in the star cluster. It's not to hard to "see" a wizard in full garb in this composition (especially in
the pure-Ha version).
The dark blobs in the nebula (best examples are a bit above and to the left of center) are Bok globules; click here to learn more about them.
The nebula is about 8000 light years from Earth and is roughly 100 light years across. Visually, it is a bit wider than a full moon.
I have presented this object in five 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); note that you can also click on the link in the Ha image to compare the Ha version to the OIII and SII versions, and you can
click on the link in the SHO version to compare two popular ways of presenting SHO data:
(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);
(ii) A version 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 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. To compare this to
another popular way of presenting SHO data--converting the green to a tan/orange, click here);
(iii) 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; you can click
on the link here to compare the Ha, OIII and SII versions;
(iv) A bi-color version (almost true-color version; the bottom photo in the stack), in which "red" is a mix of predominately ionized hydrogen emissions (Ha), with a bit of
singly-ionized sulfur emissions (SII) added (Ha and SII both emit in the red part of the spectrum), 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);
(v) A true-color version, 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.
These are the most frequent ways images of emission nebulae are likely to be presented, so I thought it would be fun to include all of them, to be able to compare and contrast the different presentations.
The "true color" version which includes narrow-band data is, to me, the most beautiful of the lot, so I put it at the top; the narrow-band data adds contrast and detail to the image, and makes
the stars smaller, which is pleasing to me, while maintaining the "true color" nature of the data. The Hubble palette version is also very pretty, and it's nice to include the (relatively sparse)
sulfur emissions that I spent a bunch of hours gathering.
The grayscale Ha image is, to me, striking in its smoothness (and the gray, of course, is the color you see when you look at this through a telescope); the other two grayscale images are interesting
on this target because all three are significant images, and it's fun to see how different each is from the others. The bicolor is there for comparison purposes,
since a lot of people use only those two filters when creating color images of diffuse nebulae. And the traditional LRGB, without using any narrow band data, also is for comparison purposes,
to show the benefits of including narrow-band data in a true-color image (compare to the top image).
This is the second time I have imaged this target; the first time was when I was in my first months with this hobby (18 years before I took this version), with fairly elemental equipment (at least by
comparison), and from my own yard. If you want to see if there has been any improvement, click here.
Ha:OIII:SII:L:R:G:B: 510:480:450:615:255:165:220 (a total of almost 45 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, deconvolution and noise reduction) done in Pixinsight; some cleanup finish work was done in Photoshop CC.
Location: Data acquired remotely from Deep Sky West Remote Observatory, Rowe, New Mexico, USA.
Date: Images taken on many nights in September, October and November 2019. Image posted November 8, 2019.
Date: Image scale of full-resolution image: 0.56 arcseconds per pixel.
Seeing: Variable over that time period, with individual calibrated luminance frames varying from 2.2 to 2.7 arcsecond FWHM; the integrated luminance image had a FWHM of 2.4
arcseconds, deconvolved to 1.5 arcseconds.
CCD Chip temperature: -25C
Copyright 2019 Mark de Regt