Sh2-88, also known as Sharpless 88, is an emission nebula, in which star-forming is taking place. The emission nebula 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.
This object is visually located in the plane of the Milky Way, which explains the immense number of stars in the field--we're looking through 7000 light years of stars at this region (not to mention many thousands of light years of stars in our own galaxy beyond this region). The various versions of this image (see explanation just below) show significantly different amounts-and sizes--of stars, depending on the mix of broad-band data (L, R, G and B, with, respectively, 300nm, 100nm, 100nm and 100nm of band pass), which allow a lot more light through than do the narrow-band filters (Ha has 7nm band pass; OIII 8.5nm and SII 8nm). The current fashion is to eliminate or minimize stars, but I like a dense star field in an image, so I like the LRGBNB version (with predominantly broad-band data) better than the HOO version (with only narrow-band data. And I prefer the LRGBNB over the pure LRGB version because of the way the narrow-band data make the nebular regions much more vivid.
To the left of the main nebula are two bright red blobs called Sh2-88A (below/right) and Sh2-88B(above/left). Sh2-88B is an active star forming region.
The main nebula is about 7000 light years from Earth and is roughly 60 light years across. Visually, it is about the same width as 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:
(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 bi-color version (almost true-color version; the second 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, with a bit of Ha added to the blue (because where there's hydroge-alpha--red--there also it hydrogen-beta, which is blue). 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 by copying the stars from the true-color version above into this version). Even without substituting RGB stars, 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.
(iii) 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.
(iv) 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 in the structure.
(v) 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 amost completely de-emphasized in this rendition because they would be so dominant otherwise, with the entire nabula just being green). Consider that everything red in the first two images would be green in this one if I had not largely ignored the Ha data; the yellow/brown parts of this one show sulfur emissions, and the blue show oxygen emissions.
Copyright 2020 Mark de Regt